Ballistics - Kolbe on Long Range Ballistics

Comments On Long Range Ballistics
by Geoffrey Kolbe, Border Barrels
Updated version of the article: click here.

Some History In 1907, a great revolution took place in match rifle shooting. For some time the .303 cartridge with a 'Palma' 225 grain bullet had been almost ubiquitous along the firing point. (In those days, any 'military' cartridge was allowed.) Despite its great weight, the bullet had the Metford shape, which was very blunt, and this resulted in a ballistic coefficient of only 0.44 which, combined with a leisurely muzzle velocity of 2350 ft/sec. made for very poor performance beyond 1000 yards.

Meanwhile, the Germans had been experimenting with pointed bullets of the sort which we are familiar with today, and discovered that they had a great deal less drag than the blunt bullets used hitherto. Today, it is difficult to imagine the shock wave that went around the world as the results of these experiments became known. A certain Captain Hardcastle (whose name was to become quite familiar in the shooting world) had access to bullet making plant at the Chilworth Gunpowder Company and, on reading an account of the German results, went straight out and “... took the heaviest bullet used in .303 and put onto it the best point that I could hear of.”
The result was the 'Swift' bullet. This bullet had a 14 caliber tangent ogive nose whose point had a radius of .020". It was flat based, (the advantages of boat-tails were not discovered until much later), and weighed in at 225 grains. Its ballistic coefficient was 0.67, giving it only two thirds the drag of its 'Palma' counterpart.

History relates that on 29th of May, 1907 Hardcastle shot the English Eight meeting at Bisley as a Tyro, using the 'Swift' bullet. In a strong right hand wind he won the match with 135 out of 150 points - second place scoring 129. In the Scottish meeting, a new world record of 223 out of 225 was scored using the new bullet, (though not by Captain Hardcastle). The Cambridge Match was won without a point being dropped and when the Bisley meeting opened on July 8th, everybody had changed over to ammunition with the 'Swift' bullet!


I relate this little tale because for many years now the ubiquitous bullet seen across the range in MR shooting has been the 190 grain Sierra Match King. Its ballistic coefficient is 0.56, giving it 20 % more drag than the 'Swift' of 90 years ago! Surely, surely we can come up with something better?

Of course we can. But curiously, I find MR shooters very reluctant to move away from the 190 Sierra they know and love, throwing up all sorts of excuses and spurious advantages that the 190 Sierra gives. Anyway, I predict that there will be a revolution of the sort that happened in 1907 and that within two years, nobody will be using the 190 grain Sierra.

The best bullet for the Job
In long range target shooting, or target shooting at any distance for that matter, what do we look for on a cartridge/bullet combination? We want minimum group size and minimum wind drift. That's it. Muzzle velocity, time of flight, flatness of trajectory are not matters that should concern us - though a lot of MR shooters seem to spend a lot of time worrying about them.
In MR shooting, we are confined to using the .308 Winchester case. While there are a few wrinkles that can stretch performance using this case, which I will talk about later, the main influence on performance over which we have complete control, is the choice of bullet. The 190 grain Sierra gives good results up to 1100 yards, where it is still supersonic, but as it goes subsonic on its way to 1200 yards, the group size can increase dramatically. The standard solution to this problem has been to increase the powder charge to primer popping proportions, trying to keep the bullet supersonic at 1200 yards.


Alas, it has all been in vain. John Carmichael has recently masterminded a wonderful set of ballistic measurements in which he and his team have measured the down-range velocities of a variety of bullets at ranges of up to 1200 yards. The results for the 190 grain Sierra are shown in Table I. It can be seen that despite running at chamber pressures of 50,000 psi, (quite stiff!!) velocities at 1200 yards were still subsonic. It is easy to see why people thought they were supersonic at 1200 yards when we look at the predictions using Ingalls tables based on the Mayevski drag curves. (So why are the Mayevski drag curves still used? - See my article in the 1995 Spring NRA Journal). In these, predicted 1200 yd. terminal velocities, at 1200 ft/sec., are comfortably supersonic and achievable with a 2700 ft/sec. muzzle velocity.

Table l: Measured velocities through the ranges (Courtesy JH Carmichael),


By way of comparison, Table I shows predictions for the 190 grain Sierra using the Powley drag curve and also the those predicted using the Pejsa drag curve. I leave you to decide which is the best fit - but both are a vast improvement on the almost-always-used Mayevski/Ingalls drag curves. So the 190 grain Sierra bullet is not supersonic at 1200 yards out of a .308 Win case and never has been in the history of MR shooting, despite the use of excessive loads to try and make it so. How do we get around this problem? Well, have a look at Table 2.


This shows computed muzzle velocities, terminal velocities and wind drifts for a variety of bullet weights fired from .308 Win cases in a 30" barrel. A bullet form factor of i = 0.51 and a chamber pressure of 50,000 psi. is assumed. The Powley drag curve was used to predict 1200 yard velocities. The table was created using a bullet shape which is pretty constant across the Sierra range; namely an 8 caliber tangent ogive nose with a .050" meplat and a boat-tail. Sierra change the weight (and so ballistic coefficient) of the bullet by essentially just adding more length to the parallel part of the bullet. This is modeled here by keeping the form factor the same at 0.51 and, of course, the diameter the same at .308". The ballistic coefficient then just depends on the bullet weight. The result is quite striking. As the bullet weight goes up the muzzle velocity goes down - as expected, but the terminal velocity goes up and the wind drift goes down as we increase the bullet weight. And there is no apparent turn over where the bullet weight gets so big that the long range ballistics suffer.

You do not believe me? Look at Table 1 again and see what John Carmichael measured using the 210 grain Berger bullet: lower muzzle velocity, but higher terminal velocity, just as predicted.
You should not be afraid of using big heavy bullets whose muzzle velocities are sauntering rather than stupefying. The .303 British case has a capacity very similar to the .308 Win. and yet, as we have seen, our forefathers were quite happy to use bullets much heavier than anything MR shooters are willing to contemplate today. 250 Grain Sierra bullets are still available and if you used these you would be 90 ft/ sec. faster than the 190 Sierra at 1200 yards in the same rifle (provided it had an 8" twist barrel) and using the same amount of (somewhat slower) powder to give you the same chamber pressures.

But it has long been known that there are much better nose shapes than the 8 caliber tangent ogive. Secant ogive bullets were played with by Hardcastle and it is now known that in general, a bullet with a secant ogive nose will have less drag than one of the same weight but with a tangent ogive nose of the same length. Bullets of this shape have been available for a while as VLD (Very Low Drag) bullets and more are on the way. They offer significant advantages over tangent ogive Sierra type bullets of the same weight. For instance, a 208 grain .30 cal. bullet with a tangent ogive nose and a ballistic coefficient of 0.75 available from Wayne Anderson, an American manufacturer. I know that Berger has a 230 grain bullet on the drawing board with a ballistic coefficient of 0.85. Under Table 2 conditions the 1200 yard velocity for this bullet would be 1331 ft/sec. and the 10 mph wind drift 7.4 minutes. Now there is a bullet you can drool over!
The lesson to learn here is summed up in my first aphorism:
'When choosing a bullet for long range target shooting, find the bullet with the largest ballistic coefficient and use that. If there are two bullets with the same ballistic coefficient, use the lighter one'

This, of course, is just a restatement of Hardcastle's criterion of 90 years ago.
Squeezing the best ballistics from your Match Rifle (and staying legal)
The thing to emphasize straight away is that you gain little by increasing the muzzle velocities using the highest-chamber-pressures-the-rifle-will-stand route. The faster a bullet goes, the faster it slows down. Extra velocity gained at the muzzle does not translate to extra terminal velocity of the same amount. For example, take the 190 grain Sierra bullet. When pushed with a moderate load in a 30" barrel you will get about 2600 ft/sec. At 1200 yards the velocity will be around 1010 ft/sec. and the wind drift for a 10 mph will be 12.3 minutes. Now stuff the powder in until the primers start to pop and you will get about 2700 ft/ sec. for your muzzle velocity - an extra 100 ft/sec. But at 1200 yards your terminal velocity has only gone up by 50 ft/sec. to 1060 ft/sec. and the wind drift for the same wind will be 0.8 minutes less at 11.5 minutes. Given that your group, at this range, will be no smaller than a minute of angle (with this bullet), it is doubtful if you would even notice the difference. Where you will notice the difference is in the life of your cases and your barrel!

It is very important, in Match Rifle shooting, to minimize the instabilities that every bullet suffers in flight. Like a gyroscope, the bullet will yaw and precess as it spins on its way down the range. A certain minimal amount of this precession is required to keep the bullet 'tracking', keeping it pointing along its trajectory. If the bullet did not precess and went completely to sleep' then it would maintain its launch angle throughout its trajectory, which means that on the final part of the flight, when it is descending, it would still be pointing up, thus presenting a much larger cross section and substantially increasing drag. This is the extreme case of what happens when the bullet is spun so fast that the stability factor “s” is greater than about 3. The gyroscopic forces will prevent the bullet from tracking and the drag goes through the roof for the final part of the trajectory. If the precession is greater than that required to keep the bullet tracking then the result is again an increased effective cross section, giving increased drag and leading to disappointing ballistic performance.

To keep precession at the right level the first thing is to keep the stability factor from around 1.1 to 1.5 for your bullet of choice. Do not use the Greenhill formula to calculate the rate of twist you need, use of this formula is pretty much guaranteed to give you a twist that will stabilize the bullet. But, especially with secant ogive or VLD bullets, Greenhill's formula can suggest twists that will overstabilize the bullet, preventing it tracking well at long range. The computation is not a trivial one, but there are computer programs available which will do this.

The next thing is to minimize in-bore yaw and keep good control of the launch ballistics. What am I talking about? If the bullet assumes some angle inside the barrel then you have in bore yaw. This is not good because on launch (exiting the muzzle) this yaw translates into precession and so increased drag. Secant ogive VLD bullets seem particularly susceptible to this problem and this may be overcome by loading the bullet out to such a length that the bullet touches the lands in the throat of the barrel. This keeps the bullet well centered on entry into the barrel. It is, of course, also important to load the bullet using an in line seating die or some method that keeps the bullet straight when loaded into the case.

You will also reduce your SD's by using some form of bore lubricant, usually molybdenum disulfide in some form. The new 'Black Diamond' range of ammunition from Norma uses the NECO process of coating the bullets with a film of molybdenum disulfide, but you can probably do just as well by smearing a little molybdenum disulfide grease around the junction of the bullet and the case neck of your loaded rounds.

Launch ballistics are what happens when the bullet exits the muzzle. A blast of supersonic gas washes over the back end of the bullet and if there is much turbulence or the gas flow is not even over the bullet then it can be upset, inducing yaw and subsequent precession which as we now know, is bad for drag. Boat-tail bullets suffer more from this than flat based bullets, which is why flat based bullets are generally more accurate than boat-tailed ones. The back end of a boat-tailed bullet spends relatively much more time `exiting' the muzzle than a flat based one and so there is more time for the bullet to upset. A good, even crown will ensure that the gas flow over the bullet is even. The 11 degree, so called 'Bench Rest', crown provides a good interface with the boundary of the shock wave from the escaping gases, (so the theory goes), and so minimizes turbulence. Keeping the muzzle pressures down also results in better launch ballistics. Using faster powders gives you lower muzzle pressures, but usually at the expense of muzzle velocity. Or you can use a longer barrel. Longer barrels will give lower muzzle pressures with the benefit of increased muzzle velocity.

Barrels longer than 30" do not result in vast increases in muzzle velocity for the .308 Win. case. For example, a 35" barrel will give you about 50 ft/sec. more than a 30" barrel. The stiffness, (and so inherent accuracy), of the barrel decreases as the fourth power of the length. It does not take many extra inches to give you a barrel with all the stiffness of a piece of spaghetti! But... you do get lower muzzle pressures which helps the launch ballistics and, by way of a bonus, the SD of the MV's seems to drop dramatically too. The weight limit (in the rules) for a Match Rifle barrel is the limiting factor on how far one can go in this direction, but stiffness can be maintained to a degree by the use of heavily fluted barrels. Another solution is to bed the rifle on a barrel block situated in the middle of the barrel, instead of on the action as usual. This reduces the effective cantilever length of the barrel substantially and so greatly increases its stiffness. This technique is much favored by 1000 yards bench rest shooters, who look for ten shot group sizes of the order of 3" or better! MR barrels are now being fitted that are over 34" long, early indications are that these barrels give much enhanced performance, at 1200 yards, over a 30" barrel.

As I write, the Match Rifle committee seems set to introduce a chamber gauge into which your empty case (or loaded round) must fully enter. This is to police the rule which says that you must use a standard .308 Win. or 7.62 x 51 Nato chamber. The gauge is reamed to the maximum dimensional tolerances of the chamber drawings that fall within the rule. By fire-forming cases in such a chamber it is possible to get about 4 % extra volume over a case of standard dimensions. This means you can get two grains more powder into the case, which translates, for a 200 grain bullet, to a muzzle velocity 50 ft/sec. greater Extra case volume can also be created by having the throat of the chamber pushed forward so that the bullet is only minimally held by the neck. By pushing the throat forward 0.1 " over a standard chamber you gain about another 3 % of volume and another 40 ft/sec.

So what sort of performance can we expect, using fire-formed cases in a 34" barrel with a chamber reamed to the maximum size permitted and the throat pushed forward as far as we dare? We can then shovel in enough powder to give us a stiff 50,000 psi chamber pressure that does not leave us poking about for dropped primers. For a 210 grain bullet, the muzzle velocity would be about 2660 ft/sec. and for a bullet with a ballistic coefficient of 0.75 we should expect a velocity of 1350 ft/sec at 1200 yards, comfortably supersonic. It should be extremely accurate and all without the proof load chamber pressures to which some find it necessary to resort. Wind deflection for a 10 mph wind is just 7.7 minutes. This wind drift is only two thirds of that experienced by the 190 grain Sierra from a 30" barrel, putting this another way, the drift to be expected from a 190 Sierra at 900 yards! All this is possible - Today!

Conclusion
Technologically speaking, there is a lot more juice to be squeezed out of the Match Rifle rules than most people seem to appreciate. I hope this will have given you a flavor of what is possible within the MR rules. I have not even talked about what you can do with sabotted ammunition, (which, although in fact allowed under the MR rules of combat, would no doubt leave the MR committee scratching their collective heads), but that will have to wait until another time.

What cartridge should I use in my Any Rifle?
The Any Rifle match allows you to use the cartridge of your choice, within limits, and so exposes one to an agony of choice not experienced by Match Rifle purists. The process of choosing is that of comparing one cartridge case against another, one caliber against another and one bullet against all others in the various cartridge/caliber combinations! To help out, here is a second aphorism.

`Regardless of caliber, bullets of the same ballistic coefficient will have the same muzzle velocity when fired from barrels of the same length - provided the ratio of case capacity to bullet weight is the same.'

Table 3 shows what I mean. For bullets having a 0.5 ballistic coefficient I show a variety of case and bullet combinations that will give 3000 ft/sec. for a variety of calibres, all with 30" barrels. All these cartridges will have the same ballistic performance. That is the same muzzle velocity, the same terminal velocity and the same wind drift at any range.

The only assumption made is that all the bullets have the same shape and so the same form factor. But it transpires that this is a pretty good assumption across the range of target type tangent ogive bullets. If in a comparison you find that the case capacity to bullet weight ratio is higher for one combination than the other, then that combination will have the higher muzzle velocity and so a superior ballistic performance.

Take, for example, the RG Nato 7.62 ammo against a .223 Remington case loaded with a 70 grain .224 caliber Berger bullet. The RG 143 grain bullet has a ballistic coefficient of 0.42, as does the 70 grain .224 Berger bullet. The case capacity of the RG case is 55 grains of water and that of a .223 Remington case is 28.5 grains of water. Which cartridge will have the superior ballistic performance? The ratio of case capacity to bullet weight for the .223 Rem cartridge is .41 while it is .38 for the RG 7.62 ammo. The .223 Rem case with the 70 grain Berger bullet is the better combination. In fact, the muzzle velocity for this cartridge will be about 150 ft/sec. faster than the RG 7.62 ammo and so at all ranges it will have less wind drift - and also be more accurate. There have been those who have written that the .223 Rem somehow hits a brick wall at between 400 and 600 yards (depending on the author) and that there is no point in trying it at long range. On the contrary, this particular cartridge/ bullet combination will outperform the 7.62 RG ammo every day of the week!

Table 3 Comparison of calibres



This article was first printed in the Spring 1996 issue of the NRA Journal. It has been altered here to correct a few small errors and to make it more suitable as a stand-alone article.
(c) Geoffrey Kolbe 1998, all rights reserved.
Posted with permission of the author.

Ballistics - Heavy Bullets

A Long Range Competitor Looks at Heavy Bullets
by Germán A. Salazar
This article first appeared in May of 2008 at www.accurateshooter.com

A number of years ago I read an article by Dr. Geoff Kolbe, founder and owner of Border Barrels in Scotland titled “Comments on Long Range Ballistics”. Dr. Kolbe’s straightforward assertion in that article was that there is no such thing as a bullet which is too heavy for long-range (prone) shooting. This position runs counter to the widely held belief that there is a “tipping point” at which the muzzle velocity reduction caused by the heavier bullet will cause it to drift more than a lighter bullet with a higher MV. Dr. Kolbe, demonstrated in that article, that for a given cartridge (he used the .308) as long as each bullet is of similar form and is loaded to the same pressure, with a suitable powder, then the heavier (higher BC) bullet will always drift less, regardless of MV.


Heavy Bullets Work
That article made me a heavy bullet shooter and for many years my long-range rifle was a Model 70 in 30-06 with a 1:8" twist Krieger barrel shooting the 240 Sierra MK. While the recoil wasn’t for the casual shooter or for the 17 lb. AR15 types, it was very manageable and produced many match winning scores. Being somewhat experimentally minded, other projects called and the heavy bullet 30-06 fell into disuse a few years ago. More recently I’ve continued along the heavy bullet path by using the Berger 115 grain 6mm bullet in a 6XC and again, it has proven to be an excellent combination; most recently winning the 2008 Arizona Long Range State Championship with a 797-42X at 1000 yards. Whatever the caliber, heavy bullets work.

Berger Bullets has recently developed a new line of non-VLD, standard profile match bullets in various calibers. I felt this was a good opportunity to put Dr. Kolbe’s theory to the test, since Bob Jensen and I have been doing a large amount of pressure/velocity testing lately with the 30-06 in support of another project. Berger’s new line includes 175 grain, 185 grain and 210 grain bullets in .30 caliber, a perfect selection for our project. A new 30” long, 1:10" twist Bartlein barrel was fitted and chambered by Clark Fay of Raton, New Mexico and we were back in business. I should note that this barrel has a perfectly standard 30-06 chamber, no special throating for heavy bullets, although that may come later.


Reaching Max Pressure
After sorting through loads with a few powders, we determined that Hodgdon’s H4350 would produce maximum pressure levels (60,000 psi) at appropriate velocities for the three Berger bullets and a few others we brought along for comparison. We also tried H4831sc but we were unable to reach maximum pressure before reaching the limits of the 30-06 case’s capacity. There may be other powders that can accomplish the pressure/velocity combination we need, but H4350 is a well proven powder in the 30-06 and made a good choice. We used an Oehler 43 Personal Ballistics Lab with the appropriate strain gauge on the barrel to measure pressure and velocity. All bullets used in this test were moly-coated with the NECO process.

Below is a chart showing the six bullets tested, the muzzle velocity attained with each one at 60,000 psi chamber pressure, remaining velocity at 1000 yards and wind drift calculations at 1000 yards. Remaining velocity and drift are calculated using each manufacturer’s advertised ballistic coefficient. While this may not provide a perfect comparison across brands, it is certainly a valid method for brand specific comparisons are the same methodology is used to calculate each brand’s BC.





SEE TABLE AT BOTTOM

Kolbe Was Right!
Even a passing glance at this table will show that Dr. Kolbe was right on the money – no surprise there. The three Berger bullets are of the same form as each other and the two Sierra bullets are of the same form as each other and each brand’s BC methodology is internally consistent. The MV shown for each bullet is the highest that we could reach within the 60,000 psi SAAMI limit for the 30-06. Clearly, there are bullet design issues such as bearing surface length which affect pressure to a greater degree than even bullet weight.

As muzzle velocity increases, drag on the bullet increases disproportionately; thus, most of what you gain in MV is quickly lost. Note that the heavier bullets (in each type) had a higher remaining velocity at 1000 yards despite starting out slower. Muzzle velocity, like a new car, is a depreciating asset, but BC, like diamonds, is forever.

Should you immediately run out to buy the heaviest bullets available for your caliber of rifle? Not necessarily; we haven’t spoken about accuracy, recoil or chamber and twist rate suitability for heavier bullets, all of which must be taken into consideration. However, hopefully you now have a better understanding of the result of bullet choices and are in a position to make a more fully informed decision for your next cartridge/barrel/bullet selection.























Bullet





Muzzle Velocity (fps)





Velocity at 1000 Yd. (fps)





Drift at 1000 Yd. (inches)





Berger 210





2730





1611





59.2





Berger 185





2900





1605





63.6





Berger 175





2980





1593





66.2





Lapua 185 D46





2880





1548





67.9





Sierra 200 MK





2760





1498





69.7





Sierra 190 MK





2820





1472





73.0

Equipment - The CG Trigger

The CG Trigger from X-Treme Shooting Products
by: Germán A. Salazar
This article was originally published in June, 2008 in www.accurateshooter.com



Background
The CG Trigger by X-Treme Shooting Products is a Robert Chombart design, like the RPA Quadlock and the Millennium actions. The design has been around awhile, first being made in Australia and then in Great Britain where Peter Jackson refined Chombart’s prototypes and put them into production as the Jackson Rifles trigger. The trigger has been produced and sold in Europe for over 3 years now and it has gained wide acceptance. Chombart was eager to see his design sold in the US; unfortunately, Great Britain’s restrictive export laws make the export of finished triggers to the US very problematic. Compounding the problem, current exchange rates would make them very expensive in the US. Chombart then contacted Tom Myers of Cincinnati, Ohio, put him in touch with Jackson and discussions began in the spring of 2007. Myers, a well known Highpower competitor runs a precision machine shop in Cincinnati, Ohio and had all of the specialized machinery needed for full scale production of the triggers.

As an initial test, Myers made some sample sear levers on his wire EDM machinery. Those who know Myers won’t be surprised to learn that the sear levers were better than what Jackson Rifles was currently getting from their local supplier. It didn’t take long after that for a deal to be struck for the triggers to be manufactured in the US in their entirety. No expense has been spared in manufacturing. The trigger features a hard anodized aluminum case, stainless steel fasteners, ball bearings at all friction points and D-2 tool steel sear levers heat treated to 58 Rockwell C and wire EDM cut to .001" tolerance. The CG trigger has 3/16" tool steel sear levers, which can stand up to a lot more abuse than a rimfire trigger. While failures of Anschütz triggers on centerfire actions aren’t common on a properly done installation (for instance by Warner Tool Co.), there are many less professional installations out there which have had problems. The CG trigger let’s you avoid that expensive possibility by using a more robust trigger with the same or better feel and a drop-in installation.


Installation
I installed the CG Model 21 trigger on a Remington 40X action for this review. The installation was very simple. The trigger pins are installed before the trigger itself, which makes holding the bolt stop and spring in place much simpler than with a conventional arrangement. Once the pins are in place, the trigger is hooked on the rear pin, pivoted into place and the tensioning screw tightened into the captive nut on the front pin. This arrangement ensures that the trigger is positively located in the receiver with no movement whatsoever. Consistency of trigger operation is materially enhanced by this feature.

For all of its benefits, that front tensioning screw of the Model 21 presents one difficulty; albeit a minor one. The stock inletting will typically have to be deepened in the area of the screw. On my stock, it took a 0.150" cut on a mill which was accomplished in ten minutes including set up time. The cut could have been made with hand tools or even a Dremel tool for those who are so inclined. The Model 22 is a version of the trigger without the tensioning screw, using conventional pin mounting, for those who prefer not to do any inletting.


Performance
The CG trigger is available in a range of pull weight from 500 grams to 1600 grams (about 1.1 lb. to 3.5 lb.). I requested a 500 gram version as my preference is for a lighter pull. However, through a relatively simple spring change, any weight within the range can be set for any trigger. The installation instructions include very detailed adjustment procedures should that become necessary. In my case, all that was needed was a small adjustment of the optional overtravel adjustment.

Dry firing the trigger several dozen times before going to the range showed a perfect consistency in the weight of pull and the feel of the trigger; I looked forward to some live fire with it.

I shot a 60 shot 500 yard prone match with the 40X in 6BR and the CG trigger and was very satisfied with its performance. In tricky conditions, I shot a 597-36X with a 3900 round old 6BR barrel. The trigger performed flawlessly, with no detectable variation in the weight or feel of the mechanism. I asked several other competitors at the match to try the trigger and they were all very favorably impressed with it. The next day, I shot another match with a centerfire action with an Anschütz trigger; there was a noticeable difference, and it was certainly in favor of the CG which broke with a cleaner feel. While this initial test was somewhat limited, about 70 rounds fired with each trigger over two days, the CG trigger showed its capabilities and I believe it will be the one against which others are measured in the future.

The CG trigger comes with a gold anodized trigger shoe in one of two forms, either a deeply curved model or a straight model which may be reversed to present a slightly curved surface. My trigger has the straight version and it was comfortable; however, I opted to replace it with an aftermarket shoe of the same pattern as I use on other rifles. The CG trigger will accept any trigger shoe made for Anschütz triggers; accordingly, you will have no trouble finding something that fits your desires as there are dozens of aftermarket Anschütz pattern trigger shoes.

Update - June 2009Since the initial writing, I installed a second CG Model 21, this time on a Long action Remington 700 in a CSS RT10 Tubegun in 30-06. With over 1000 rounds fired in the RT10 as well as another 500 or so in the 6BR 40X, I have found the CG trigger to be perfectly reliable and consistent. In all temperatures tested, from the high 30's to over 100 degrees and in Arizona's notoriously dusty conditions, the triggers have performed flawlessly and without need for further adjustment. I plan to upgrade my other rifles to this trigger over the next few years as the budget allows.

Cost
The most expensive trigger is the Remington with safety and bolt release; MSRP is $330. For the plain version without safety and bolt release, MSRP is $300. This trigger is designed to go head to head against the Anschütz for highpower rifles. With dealer cost for an Anschütz at over $300 and then the cost to modify the rifle and hang the trigger, the CG is very cost effective at $300 vs. over $500 for a potentially weaker Anschütz conversion.

Production
Myers is starting production with the Remington version (including many custom actions such as Nesikas, Pandas etc). He is also now producing RPA Quadlock triggers. He has a completed prototype of a Remington tactical trigger that fits in on 2 pins (like a factory Remington or Jewell) and will have a 3 position safety. Production for that one is slated for this summer. He is also working on the Winchester Model 70 for later in the year. Barnards are on the horizon but since they come with a decent trigger, it probably won't happen until next year.

Cartridges - 6XC: 2008 Arizona LR Championship

Salazar Captures Arizona 1000-Yard Title with 6XC and Berger 115 VLDs

This item was originally published February 14, 2008 at http://www.accurateshooter.com/


We’d like to congratulate German Salazar. He recently won the Arizona State 1000-yard prone rifle championship with an outstanding 797-42X score (out of 800 possible). Individual stage scores were: 200-08X, 198-10X, 200-14X and 199-10X.
German was shooting a 6XC with a Gilkes-Ross action and 1:7.5″ twist Krieger barrel, in a Master Class stock. German used moly Berger 115 bullets with Hodgdon H4831sc powder. Remarkably, German shot with iron sights throughout the match, even the two stages where scopes were allowed. German told us that he is “very impressed with the 6XC using the Berger 115s at 3000 fps. It is a superb choice for 1000 yards. The case capacity is good, the Norma brass is good, and the Berger 115s have great ballistics.” Interestingly, German is so taken with the 6XC/115 Berger combination that he recently sold all his 6.5-284 equipment–barrels, reloading gear, you name it. German told us “the 6XC shooting 115s at 3000 fps gives up almost nothing to the 6.5-284 in wind drift, with equal or better accuracy. So, there was no reason for me to keep the 6.5-284.” The Berger 115 VLD has a published BC of 0.595. Berger recommends a 1:7″ or faster twist barrel.

Cartridges - 6XC For Long Range Prone

A Prone Shooter Looks at the 6XC
by Germán A. Salazar
This article was originally published in the May, 2007 issue of Precision Shooting magazine.  The article also appears here: http://www.6mmbr.com/6xclongrange.html

What is the 6XC and why should we care about it? The 6XC is one of the latest in a long series of modified 22-250 cases necked up to 6mm; a legacy that probably goes back as far as the 22-250 itself and perhaps peaked in popularity with the Donaldson and Walker versions of the 6mm International. While those early efforts have faded from the scene, newer versions continue to crop up and chief among them today is the 6XC. Figure 1 shows the 6XC between the 6BR and the 6.5-284 for comparison purposes.

Most US Highpower competitors are at least aware of the existence of the 6XC cartridge; our overseas readers perhaps less so. As Vince Bottomley indicated in his article in the July 2006 issue of Precision Shooting, the 6XC is very similar to the RUAG 6x47 Swiss Match. The 6XC has been used to win the NRA Highpower Rifle National Championships at Camp Perry for the last several years by its originator David Tubb as well as by Norm Houle and Dennis DeMille. Mr. Tubb also won the 2005 NRA Long-Range Championship firing the 6XC. That achievement made an impression on many dedicated prone shooters who had previously given the cartridge little notice. Today, the 6XC is making inroads at prone matches from 300 meters to 1000 yards. This article is a look at the 6XC from the perspective of a dedicated and very active prone shooter; it is a compilation of my experience, observations and opinions of the cartridge’s advantages and disadvantages for prone shooting only. As with all opinions, yours may well differ from mine and there’s certainly nothing wrong with that.

While the 6XC has been closely associated with McMillan’s Tubb 2000 rifle in which it is offered as a standard chambering, it is a simple enough matter to chamber any existing rifle with a 0.473" bolt face for the cartridge. Now that C.I.P. standardization is in place and Norma is prodcing brass, I expect other makers to follow. My test rifle for this article is a Winchester Model 70, stocked by Alex Sitman of Master Class Stocks about ten years ago and recently barreled by Clark Fay of Raton, New Mexico with a Krieger 6mm, 1:7.5" twist barrel in the now ubiquitous 30" medium Palma contour in place of its former 30-06 Krieger.


Chamber Reamers
6XC chambering reamers are available directly from Pacific Tool & Gauge (PTG) as well as from Hugh Henriksen. I ordered a reamer from PTG with a 1°30" leade angle and a 0.271" neck diameter (see Figure 2). The standard Henriksen reamer is made with a 0°45"leade angle and a 0.276" neck diameter. While the shallower leade angle seems to be gaining some popularity in various Highpower oriented reamers, I have yet to see a cogent explanation of why it might be better. There are those who argue for and against the shallower leade angle each claiming that it will give longer or shorter throat life, more or less accuracy. Until I see a valid direct comparison, I will remain tradition-bound at 1°30". I selected the 0.271" neck diameter based on the neck thickness of Norma 22-250 brass as I wanted a reasonably close fit without neck turning; this gave me 0.004" clearance. Subsequently, when the Norma 6XC brass became available I found this dimension to be too tight as the 6XC brass has a slightly thicker neck. Turning the 6XC case necks to 0.013" solved that problem.

Brass
The brass cartridge case is, of course, the heart and soul of any discussion of a new cartridge and in the case of the 6XC it has also been its Achilles heel. Whether forming cases from 22-250 and putting up with the same donut problems that have plagued reformed 22-250 cases since the time of Harvey Donaldson, or trying to buy Tubb 6XC brass as offered by Superior Shooting Systems (SSS), the life of the would-be 6XC shooter hasn’t been a bed of roses. Over the past three years, there have been three separate batches of this US made brass and all have different internal volume so proceed with caution on load data when using Tubb headstamp brass. To further complicate matters, delivery times on orders have at times exceeded two years aggravating potential customers to the brink of despair. More than one competitor I interviewed gave up on the 6XC over the brass issue.

In August, 2006, however, Norma began importing 6XC brass into the US and it is of their usual high quality. Delivery of the Norma brass remains a single source proposition for the time being; hopefully the supply issues that have dogged SSS in the past will be overcome and delivery times will come into alignment with the rest of the industry. Far better would be for Norma to distribute this brass through all of their usual distributors; we can only hope for such a decision to be made.

It is fair to say that the majority of brass being fired in 6XC chambers today is reformed 22-250 brass of various makes. Remington, Winchester and Norma 22-250 brass are readily available and all are suitable for reforming; we will examine all three (see Table 1).

Prior to the arrival of the Norma 6XC brass, my primary choice in brass was Norma 22-250 because of its great uniformity in case and neck thickness as well as weight and volume. Norma is somewhat more expensive on initial purchase than the others but that difference is minimal when amortized over the life of a case and worthwhile for the higher quality. I have fired one set of Norma cases twelve times with full power loads with no detectable loosening of primer pockets, neck splits or any other form of case failure or fatigue. The Norma 22-250 brass tends to form a donut in the lower portion of the neck after fireforming which can be reamed out with a K&M neck turning arbor with the carbide cutter. I have also detected the donut in Winchester brass, but not in Remington; however, I should mention that I have used far less of those brands and different lots may provide a different result.

Three fundamental changes are made to 22-250 brass in the process of becoming 6XC: the neck is expanded to 6mm, the shoulder is pushed back and the body taper is greatly reduced. Fortunately, 6XC case forming is as simple as any reforming operation can be; one simply runs a 22-250 case into the 6XC sizing die and out comes a case suitable for firing in competition, albeit appearing somewhat malformed. After forming but before firing, Winchester brass displays the characteristic mushroom shape at the shoulder, whereas Remington and Norma brass are not quite as dramatic looking (see figure 3).


For those who can’t abide the thought of mushroomed cases, Larry Medler has developed a simple “No-Mushroom” process which he details on his web page: (see figure 4) While Larry’s method is interesting and produces cases that present a more pleasing initial appearance, once the first firing takes place and the case blows out to its final dimensions, the initial shape is moot.

The new Norma 6XC headstamped brass is what everyone has been waiting for and the initial lots I received live up to the expectation. I got 200 cases from Swedish competitors at the 2006 ISSF World Championships in Zagreb through a friend who was there and another 300 cases through the US distributor. Both lots are of very uniform construction with suitably uniform necks (less than 0.001" variance). Internal volume is slightly greater than the reformed Norma 22-250 brass and weight is proportionately lower (See Table 1). After four full power 1000 yard loadings, the 6XC headstamped brass shows no signs of expanding primer pockets. I intend to keep firing the same 70 cases until they show some signs of fatigue but I can’t predict if or when that will occur. One real benefit of the 6XC brass is the lack of donuts forming in the necks as compared to the reformed 22-250 brass. This is especially useful when firing 115 grain bullets as these tend to have their shank far down the neck into the donut area.


Internal capacity of Remington 22-250, Winchester 22-250, Norma 22-250, Norma 6XC and Tubb (3rd Generation) brass (all after fire-forming) is very close, allowing safe interchange of load data between these brass types. However, first Generation Tubb brass is very heavy (approx. 172 grains) and has much less case capacity – it is not suitable for the loads discussed in this article. I have not been able to locate any Tubb 2nd Generation brass for measurement.


Norma’s new 6XC brass uses a large rifle primer and a standard 0.080" flash hole as does all the 22-250 brass and the Tubb headstamped brass (see figure 5). Many of us who were waiting for the arrival of the 6XC brass hoped it would use a small rifle primer and a 0.065" flash hole like the 6BR and 6PPC; alas, that was not to be. Interestingly, Lapua chose the small primer path with their new 6.5x47 brass which is very similar (nearly identical, actually) in capacity to the 6XC. While I might wish for the small primer case in 6XC, the reality is that for 600 to 1000 yard shooting, the performance of the 6XC has been so good that it would be churlish of me to do so. At 300 meters on the ISSF target, however, every little bit helps and a I believe a small primer would be worthwhile.

Components
When developing loads for a new (to me) cartridge, I prefer to standardize on a few components to keep variables to a useful minimum. Hodgdon’s H4350 and H4831SC are the most widely used powders in the 6XC and were the primary powders evaluated here. Both of these powders’ burn rate sand bulk densities are well matched to the volume of the 6XC case with bullets in the 105 to 115 grain range.

Along the same lines, the Russian primers sold under the PMC label, have proven themselves to me in various calibers to have more uniformity in ballistics and more resistance to blanking than other types and they have become my standard primer. CCI-BR2 primers are a useful alternative.

Bullets are the big choice when it comes to most cartridges and this one is no exception (see Table 2). I normally shoot Berger bullets and their 105 VLD has proven to be an excellent choice for the 6XC. As I have always noted with Bergers, bullet weight and bearing surface length are very consistent. I do not routinely check these items on Bergers because their quality control is more than adequate; something that can’t be said for all large bullet makers. In my rifle, I can drive the 105 VLD at just over 3000 fps with accuracy almost equal to the 6BR at 2750 fps (my pet load). This achieves my initial goal with the 6XC which is to drive the same bullet I use in the 6BR to a significantly faster muzzle velocity without getting into dangerous pressure levels and without a big reduction in accuracy. Reduced barrel life compared to the 6BR will be the main trade-off, but that’s a fair price to pay for the added velocity.

Hornady’s 105 grain AMAX bullet is another good choice but I have only done a limited work-up on it at this point. The most intriguing bullets for the 6XC, however, are the Berger 115 VLD and the DTAC 115 grain bullet manufactured by Sierra. One of my goals in the preparation of this article is to give a useful comparison of the 105 and 115 VLD Bergers and the 115 DTAC bullets at 1000 yards with loads tailored to each.

Other bullets shown in Table 2 were evaluated and shot in the 6XC to some extent, but none equaled the accuracy and low wind drift of the Berger 105 and 115 in my testing and thus the focus of the test was kept on those two bullets. Readers should take a close look at the bearing surface length for each bullet as this has a measurable effect on pressures with a given load. A load that is maximum with a short bearing surface bullet may be in dangerous territory if a longer bearing surface bullet is substituted without a reduction in charge weight.

Dies
If there is one area of the 6XC project where I was initially frustrated, it was the loading dies. SSS offers a full-length sizing die packaged with a Redding Competition seater die. The seater is a typical Redding Competition Series die and works perfectly, leaving nothing to be desired in the way of improvement. The same cannot be said for the full length sizing die in the package. To be clear about the source of my frustration, I do not shoot any course of fire requiring rapid fire; my concern is purely with deliberate, precision shooting from the prone position at various known distances from 300 meters to 1000 yards. Accordingly, I prefer a full length bushing die that sizes the case minimally, a good selection of bushings and I also like to have a neck sizing die. None of these is possible with the SSS die set which uses a non-standard neck/shoulder bushing (available in only two sizes) and sizes the base of the case very aggressively (see figure 6). If one is an advanced reloader, a specialized die with multiple interchangeable non-standard parts for sizing (such as the highly regarded multi-caliber FL die from Warner Tool Company) can be acceptable. However, as this is the only generally available full length die in 6XC, it would have been much better for SSS to stay with the standard 0.500" diameter Wilson/Redding type bushings.

When the 2006 Redding catalog arrived I noticed that they planned to offer 6XC dies in various configurations. Since Redding dies are my usual choice, I was very excited at the prospect of getting dies that use my existing supply of bushings and that, perhaps, would be dimensioned more appropriately for my purposes. Redding now offers their Type S Neck Sizing bushing die, a body die and their Competition Seater as a set or individually as well as in the set (see figure 7).


I ordered the new dies and after a delay of some months while production cranked up, the Redding Type S bushing neck die and body die arrived. What a pleasant experience it was to have dies that work in the usual manner, don’t distort the brass and accept my existing supply of bushings. While a Type S full length die would be nice to have as well, I won’t quibble with Redding’s decision not to make that at this time as they have solved my problems with what they are making.

Unlike the Redding dies, the SSS non-standard neck bushing incorporates the 30° shoulder; obviously, this does not interchange with the existing inventory of Redding and Wilson bushings that suppliers and reloaders have in their inventory. While the SSS bushing sizes the neck all the way to the shoulder rather than leaving about 0.030" unsized as do the Redding/Wilson type, to me this provides no useful gain while significantly reducing tuning flexibility since only two bushing sizes are offered (0.268" and 0.266").

Even worse than the lack of a useful bushing selection in the SSS die, is the fact that the die sizes the base area of the fired case such an extreme amount that case life will, in my opinion, be adversely affected. As supplied, the sizing die reduces the base of the case by 0.0025" to 0.0030"; in fact it even appears to be reducing the solid web of the case. Fired cases measure 0.4680" to 0.4685" just above the web; when sized with the SSS die they measure 0.4655", far more than needed to ensure reliable function for my purposes. I had the die modified by a tool and die maker and it now sizes to 0.4665" for a 0.0015" reduction and also has a smoother feel which I believe is due to a better interior finish after the polishing. The Redding body die sizes the base of the case only to 0.4670" to 0.4675", a far more useful dimension than the SSS die and one that should lead to longer brass life.

Prior to the arrival of the Redding body and neck dies, a solution to the over sizing problem was neck sizing with a Redding 6BR bushing neck die. While the interior of the die is not a perfect fit on the 6XC brass (the 6BR has a slightly larger shoulder diameter) it works well enough. If you already have a 6BR die and don’t want to reset the lock ring, buy two Redding die spacer kits part number 80901 and use both 0.125" spacers and one 0.135" spacer under the die. You can now neck size 6XC with your 6BR neck die at the same lock ring setting. My resizing procedure is to full length size with the Redding body die or the modified SSS die for a 0.001" shoulder setback using the supplied 0.266" bushing, followed by neck sizing with the Redding 6XC neck die and a 0.264" bushing. This is for unturned Norma 22-250 brass which has a loaded neck diameter of 0.267". With the Norma 6XC headstamped brass, different size bushings will be required, the exact one depending on the extent to which the necks are turned (if at all). In my case, with necks turned to 0.013" and a loaded diameter of 0.269", I use a 0.268" bushing in the FL die and follow up with a 0.267" bushing in the neck die.


Loading and Shooting
My initial load workup centered on H4350 and the Berger 105 VLD. Working up in 0.2 grain increments I went from 37.0 to 40.0 grains. Accuracy, as measured by 500 yard groups fired prone, increased with each increase in charge weight up to 39.0 grains. I stopped testing at 40.0 because the primers were just beginning to show some slight cratering, although there were no other signs of excessive pressure. Bolt lift and extraction remained the same as at the lighter load levels, primer edges were still well radiused and the base diameter of the case did not show excessive expansion. Nonetheless, at nearly 3100 fps, and with cratering starting, this is a prudent place to stop.

A similar process with the 115 grain bullets led me to a maximum load of 43.0 grains of H4831SC with both brands of 115 grain bullets. Other competitors have reported good results with this combination and it fills the case more completely. Testing at 1000 yards showed the Berger 115 to have about 2 moa less drop and more resistance to changes in wind speed. At the recent 2007 Arizona 1000 Yard State Championship and a club match the preceding week, I fired six scores of 199 and 200, all over 10X’s with the 115 Bergers and H4831SC, all but one of these scores was with iron sights. That performance was good enough to make me rethink the usefulness of the 6.5-284 which shoots no better and recoils substantially more. The recoil is a factor for me as I shoot the entire string with the rifle in my shoulder and low recoil helps maintain consistency when shooting in this manner.

The missing element at this point is testing the 105 grain bullets with H4831SC at 600 yards and below; but others have reported good results with this combination. Conversely, when I tested H4350 with the 105 and 115 grain bullets at 1000, results were not as good as with H4831SC. It appears that for the prone competitor looking for one powder for the 6XC, H4831SC may well be the best choice.


Borescope examination of the 6XC bore at 1000 rounds revealed no significant cracking of the bore surface and minimal erosion. This compares very favorably with the 6.5-284 which typically shows very advanced cracking and erosion by this stage. For comparison, I examined my current 6.5-284 barrel which had 480 rounds at the same time and it was definitely in worse shape than the 6XC with twice the rounds fired. Given the performance of the 6XC at 1000 yards, I believe the comparison to the 6.5-284 is more relevant than to the smaller cartridges such as the 6BR. Obviously, the 6XC will have a shorter barrel life than the 6BR, but at this point I can’t determine how much shorter. I typically see 3500 to 4000 rounds fired on a 6BR before accuracy at 600 yards becomes suspect, I would imagine the 6XC might go 2500 rounds or so based on what I’ve seen so far, but that is nothing but raw conjecture.


Conclusion
After shooting the 6XC for one year at various distances and under wind conditions ranging from mild to severe; I can say that it is a great choice for 600 and 1000 yard matches. In fact, if I could only have one cartridge for 300 Meters to 1000 yards, this would likely be the choice; thankfully that’s not the case. In ISSF type 300 meter prone matches as well as 500 yard prone NRA matches and most 600 yard matches, I believe the 6BR with the 105 Berger VLD is still a better choice for pure accuracy. The 6XC’s greatest virtue, reduced wind drift with 105 and especially 115 grain bullets, is less of a factor at these distances than on a blustery 600 yard range and at 1000 yards, and at those longer distances, it is a winner and worth the effort.

SCROLL DOWN FOR TABLES







Brass Type


Water Capacity (Grains)


Avg. Case Weight (Grains)


Neck Thickness


Loaded NeckDia.


Norma 6XC


49.3


157.7

0.0135"
± 0.0004"


0.270"


Norma 22-250

47.8

161.2

0.0121"

± 0.0002"

0.267"

Remington 22-250

48.4

154.9

0.0135"

± 0.0010"

0.270"

Tubb 6XC (3rd Gen)

48.6

151.1

0.014"

± 0.0005"

0.271"

Winchester 22-250

48.7

161.7

0.0135"

± 0.0005"

0.270"








Bullet

Diameter

OAL

Bearing Surface

105 Berger VLD

0.2432"

1.237"

0.368"

105 Hdy. AMAX

0.2434"

1.230"

0.450"

105 Lapua Scenar

0.2430"

1.252"

0.450"

107 Sierra MK

0.2432"

1.227"

0.415"

108 Euber

0.2428"

1.218"

0.490"

115 Berger VLD

0.2431"

1.333"

0.414"

115 DTAC

0.2436"

1.293"

0.480"
 

All contents Copyright 2012 The Rifleman's Journal