Equipment: Palma Bullets and Barrels

The following is a question from a friend and my answer to him.  I'm posting them here because it's a very good question for the newer Palma shooter and hopefully the answer will provide the information needed when making a decision about bullets and barrels.  -GAS-

Palma Bullets and Barrels - A 2010 Overview
By: Germán A. Salazar

Germán ,

I just ordered my stock from Gary at CSS, looking forward to that arriving. While I am waiting, I am searching for the right barrel for this rifle. Since it will be used for Palma and High Power I am not too worried about just shooting 155's (I will not be shooting International Palma). I am looking at the 10-12 twist range, but am open to ideas. What my real question is about is the groove/bore diameters out there. Should I go with a tight 0.307" x 0.298" or stay with a 0.308" x 0.300" offered by many barrel makers. What are your thoughts on this and how many grooves in a barrel? I need someone to give me a start since I have formed no opinions yet. I have read a lot on the internet, but cannot find too much useful information on this topic. Thanks and have a great weekend.

Jonathan


Hi Jonathan,

That's a good question that deserves some thought, more people should ask.

As a bit of background, except 1976, Palma matches were shot with military ball ammo until the 1992 match.  The British continued to shoot ball until about three years ago, and because the bullets in ball were typically 0.306" to 0.307", the need for those tight barrels arose in order to get any sort of accuracy with them.  The same bad bullets are the root of the use of the 1:13" twist, as the faster you spin a bad bullet, the more likely it is to fly off course; good bullets such as current Sierra, Berger, Lapua, and other modern match bullets are very tolerant of spin rates in excess of that which is minimally required to stabilize them.  In other words, you can't spin good bullets too fast in a .308 so a slow twist is not required.  The only potential danger in spinning too fast is bullet blow-up and that isn't going to happen with a .30 caliber bullet at .308 velocities for reasons too involved to get into here.

With the introduction of the Sierra 155 bullet, which was designed for the 1992 Palma ammo loaded by Bob Jensen, the bad ammo era came to an end for the actual Palma match and there began a sea change in ammunition for all Palma shooting that is now complete - ball ammo is no longer shot in Palma shooting anywhere.

So now all that is ancient history internationally and more importantly to you and me, it is irrelevant to the American shooter who doesn't want to travel overseas. We have an incredible selection of .30 caliber bullets and there is no sense in choosing a barrel that limits one's choices. Let's think about a few possibilities. First bullets, then barrels to match.

Let's not rule out the 155; actually, there are some incredibly good 155's out today. My favorite is the Berger 155.5 Fullbore bullet; I consider it to be the most accurate 155 ever made. With the right load, this bullet is as accurate as any .30 caliber bullet and the wind drift is no worse than any normal weight (155 to 190) bullet other than the new Berger 175 and 185. When I run the numbers on the Berger 155.5 at 3000 and the Sierra 190 at 2640 (both are my true MV for each bullet) they come out essentially identical. Same happens if I compare them at 2800 for the 190 and 3150 for the 155 which is what I could do with them from the .30-06.

The Berger is a great bullet, but it isn't the only 155. The plain old Sierra 2155 is still a very accurate bullet and at 300 to 600 yards is worth shooting. It is the most wind sensitive of all the 155's but it's also reliably accurate. Besides, a little extra wind drift at 600 isn't a terrible thing, it'll keep you busy on the windage knob and seriously, that's good practice for any Palma shooter. The Nosler 155 is a good clone of the Sierra 2155. The Lapua 155 is an excellent bullet as is the new Sierra 2156, but I prefer the Berger to these although many shooters are using both of them with very good results.

Next is the Sierra 168 which can be used at 300 yards and should really go no further than that. Frankly, as good as it is for short range, there are better bullets and the only reason I can think of to shoot the 168 today is to use up an existing stock of them. Never shoot a 168 past 600 yards, it is absolutely impossible to keep it supersonic at 1000 from a .308 and it's flatly terrible at 800 and 900. It's no great joy at 600 either, you're always better off with something else.

The 175 class of bullets is next and right there is my current favorite overall Palma bullet, the new Berger 175 BT. The 175 is a slightly lengthened version of the 155.5 Fullbore and has shot very well for me in both .308 and .30-06 in barrels with twist rates of 1:13", 1:12", 1:11" and 1:10" as I would expect a good bullet to do. The wind drift on the 175 is less than the 155.5 when both are loaded to the same pressure level (the MV will be lower, but if pressure is the same on two bullets of the same type, the heavier will drift less). I shot the 175 Berger in the recent Arizona Palma Championship and finished well with it. I use H4895 powder with it. I haven't shot the Sierra 175 in a long time and never in a Palma so I can't comment on it, but I suspect that it does not have the aerodynamic characteristics of the Berger. You can check into that by running some numbers on them at JBM Ballistics select the Litz data for each bullet from the bullet list (it'll be obvious when you're there).

The new 185 Berger has been winning a lot of Palma matches, and is the current choice of Bryan Litz who is certainly a top Palma shooter. It says a lot that this is the bullet Bryan chooses for his own shooting since he is Berger's ballistics chief. Mid Tompkins shoots it also and he's a pretty sharp guy as you probably know. Theoretically, based on drift, this is the best Palma bullet available today. I have a few boxes and have tried them but have always felt the 175's were shooting better for me. This may simply be a case of inadequate load development on my part and that would be perfectly understandable since I tend to put loads together with small variations and try them in matches more than doing a more formalized development program. Still, the 175's have come together quickly and shot great for me, but not the 185's.

I shoot the old Lapua 185 FMJ D46 bullet a lot because I have a ton of them. However, like the Sierra 2155, it's an outdated design and not worth buying now. Burning up an old stock is fine and I shoot them at all distances. Like the old Sierra, you have to crank the windage knob a bit extra with the D46, but I don't mind. They will shoot very well in almost any barrel regardless of wear, a very attractive feature!

The 190 Sierra is my standard bullet for .30 caliber shooting. While it isn't very high in BC and it has a long bearing surface which keeps MV down a bit, it is reliably accurate at all distances and will work with a normal .308 chamber, although a slightly longer throat is a good thing but not essential. With a new barrel, I generally evaluate it's potential with the 190 and then try other things if it looks good. If it won't shoot 190's well, chances are it isn't going to shoot well at all (assuming proper rate of twist). The Berger 190 VLD is another good 190, but the 185 BT has really superseded it.

I've shot the Berger 210 and other heavy bullets in .308 but will omit them from this discussion because you really need to have a dedicated barrel for them with a 1:10" twist and a long throat. They're interesting, but a specialized area.

The bullet discussion was long because it sets up the barrel choices and allows the barrel discussion to be a bit shorter. First, all of the bullets mentioned will shoot perfectly well in a 0.300" x 0.308" barrel. I think the time for tight barrels has passed; they increase pressure and provide no useful benefit with modern bullets. Ball is dead in Palma shooting and the tight barrels should be buried alongside it.

Number of grooves is not something I place a great deal of emphasis on.  Most cut rifled barrels are four-groove although you can specify six-groove from some makers.  Bartlein and Krieger also offer five-groove barrel with some variation or other of the 5R type rifling.  Most button rifled barrels, such as Hart, are six-groove.  I have all of those variations and if there's something better about one or the other, I can't find it.  The 5R shoots and cleans well, but so do the normal ones.  I believe that a good quality barrel, properly lapped by the manufacturer, will shoot well regardless of number of grooves or groove configuration.  Theoretically an odd number of grooves should be less stressful on the bullet, so if a shooter is pushing bullets very hard and having some blow-ups, it's something to consider.  This really isn't an issue in Palma shooting with any of the available bullets; it tends to be a greater issue with high velocity, fast twist, smaller caliber rifles such as the 6.5-284.

Rate of twist is a more interesting question. As I mentioned earlier, slow twist barrels, on the ragged edge of stability, keep bullets of less than perfect construction flying slightly closer to the intended path. British shooters even liked 1:14" twist barrels for ball, again for that reason. We are shooting good bullets, so let's eliminate that consideration as we examine twist.

The rate of twist required to stabilize a bullet of a given caliber is directly proportional to its length. As bullets have become more streamlined for higher BC in any given weight category (as discussed above) they have gotten longer. Think about it a moment, the only way to increase the BC of a bullet at a given weight is to stretch the nose and maybe the boat tail to a more streamlined shape, thus lengthening it. That means that today's bullets generally should use a slightly faster twist than the old ones.

I consider a 1:12" to be the slowest desirable rate of twist for a Palma rifle today if one is not intent on shooting 155's. The 1:13" can shoot 175 and in some cases the 185 well, but it's easier to get them shooting from a faster twist. The 1:12" will shoot all of these perfectly well and in many cases the 190's as well, although that's not guaranteed.

The 1:11" twist is my general preference. It will handle all bullet weights with no concern. From a 155 to a 190, I never have to give rate of twist a second thought with a 1:11" and I can just conduct my load testing or match shooting with whatever bullet catches my eye that day (and I like to try a lot of different ones). Generally speaking, a 1:11" 0.300" x 0.308" barrel is my idea of a perfect .308 or .30-06 barrel.

The 1:10" barrel doesn't gain anything over the 1:11" for most uses because you need a long throat to shoot the 210 class bullets that the 1:10" allows you to shoot. That, of course, wipes out the barrel for light bullet use because you can't keep them in the case neck! My only 1:10" is on a .30-06 that I use for 210's on occasion - there's no good reason to use one for a general purpose .308.

What we need to talk about next is chamber reamers and they are a big topic unto themselves.

Germán
 

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