Accuracy Secrets of the .30-06 - Part 1
by Germán A. Salazar
"The .30-06 just can't beat a .308."
"The .30-06 recoils too much."
"The .30-06 case is too long for real accuracy."
"Everyone knows the military switched from .30-06 to .308 because the .308 is more accurate."
"Snipers use a .308, not a .30-06, that should tell you something."
"The .30-06 is old, out of date, an antique - you can't win matches with it."
I love hearing statements like those, it lets me know that whoever is uttering them is going to be easy pickings in a match because he underestimates the competition and won't be working as hard as he should. The .30-06 vs. .308 debate has been going on since the day the .308 was introduced to the public and probably won't die anytime soon. We've covered the .30-06 vs. .308 debate before (click here for article) with extensive data from over 6,000 rounds fired in actual rifle matches, not keyboard pounding, so we won't do that again. What we're going to discuss is how to put together a .30-06 for NRA prone, F-Class, tactical or other recreational matches that will be competitive, reliable, long-lasting and moderate in cost.
Amazingly, the .30-06, a cartridge with well over a century of unmitigated success on the range and in the field is rarely seen on the Highpower range these days and is poorly understood by a generation of shooters raised on plastic rifles firing cartridges nearly suitable for rodent control. The .30-06 conquered the 1000 yard ranges from Camp Perry to Quantico, from Camp Pendleton to Fort Benning and all points in between - not to mention the battlefields of Europe in two World Wars where the average firing distance was long and the stakes immeasurable. Yes, history matters, in real life as well as in competitive shooting and the .30-06 is most certainly not a dusty relic of history; it is an accurate, powerful cartridge, capable of exceeding it's many offspring in any measure of ballistic performance. Beating the baby cartridges with the .30-06 doesn't take any voodoo or exotic components, just attention to details and the careful application of a century of accumulated wisdom.
There's no getting around this basic fact: you need a top quality barrel to get top quality accuracy. The barrel is the heart of the system and no mass-produced barrel is going to perform on a par with a Krieger, Bartlein, Hart, or other performance barrels made specifically for accuracy. If you're working with a factory or arsenal barrel, the end results will be somewhat limited, but you can still outshoot the ,308 and others with similar factory barrels; we'll cover that in a bit more detail further on, for now, let's look at new barrels.
Makers - I use barrels from Krieger, Bartlein and Hart in my rifles with no particular preference, although I find Kriegers usually easier to get as Bruno's keeps the profiles I like in stock (he has Hart and Shilen also). Krieger and Bartlein are made by the cut-rifling process whereas Hart barrels are button-rifled. I have a slight preference for the cut-rifled barrels because I believe the process is more likely to result in perfectly consistent twist rate, but my two main .30-06 rifles have Hart barrels, so this really isn't a big issue. The four items in barrel choice that genuinely matter are internal dimensions, rate of twist, length and weight; let's take a look at each.
Bore & Groove - Although it would barely seem to be worth mentioning, the bore and groove dimensions should be 0.300" x 0.308". Krieger, Bartlein and perhaps other makers offer barrels with slightly smaller internal dimensions, these are intended for chambering in .308 for international Palma shooting where issued ammunition often has bullets slightly smaller than .308" diameter. This is not a concern for the US shooter using match grade bullets and in any event not an issue at all for the .30-06. More importantly, those reduced dimensions may cause excessive pressure with some of the long, heavy bullets we prefer for the .30-06. Stick to the standard 0.300" x 0.308" dimension for your .30-06, that's what it takes.
Twist Rate - The standard rate of twist for factory and arsenal barrels chambered in .30-06 is 1:10". This was established in 1903 with the .30-03 cartridge that used the Krag's 220 gr. round-nose bullet at a very modest muzzle velocity. As the cartridge evolved into the .30-06 with a 150 gr. spitzer bullet, the original rifles had their barrels set back and rechambered with the new short-throat chamber for the lighter bullet, but naturally the rate of twist remained the same. That's ancient history and we don't need to repeat it; what we need is the optimal rate of twist for modern match bullets, and that is the 1:11" twist. This will properly stabilize bullets up to 210 gr. with no concerns and that's as heavy as we're going to consider in this series.
As a fundamental rule, the slower you spin a bullet the more accurate it can be. The reason is simply that bullet jackets aren't perfectly uniform in thickness and a slower rate of spin keeps those tiny variances from altering the bullet's flight. Think of a car tire with a slight imbalance, the faster you go, the more you feel that thumping. The bullet is the same except that because it isn't held by an axle like the tire is, the imbalance will make it wander slightly from its original path. The limitation we face on rate of twist, is that although we want it to be slow for accuracy, we need a certain amount of twist for stability. The 1:11" twist will stabilize all useful match bullets, whereas a 1:12" twist is marginal with some 190 gr. bullets and all of those that are heavier. Accordingly, we can rule out the 1:10" twist as unnecessarily fast, the 1:12" as potentially too slow, and settle on the 1:11" as being just right. Accuracy won't necessarily suffer much with a 1:10", so if you have one, that's fine, if a touch less than optimal. I would avoid the 1:12", however, because it will limit your bullet choices.
Length & Contour - Long and heavy is the rule of thumb for a .30-06 barrel. Let's start with length; I consider 28" to be the ideal length for a 30-06 barrel. This is long enough to take full advantage of the powder charge you're burning. Although a 30" barrel will give slightly higher muzzle velocity (about 25 fps) given the heavy contours that are called for, I prefer to keep the length at 28" to reduce fatigue during a string. If you're shooting F-Class or another form of supported shooting, then a 30" barrel can be worth considering, but nothing longer than that for reasons we'll discuss in a Part 2.
There is no reason to use a short (under 28") barrel on a .30-06 when you have the choice; of course, if you're working with an existing barrel that's a different matter, but you won't get quite the performance level of the right-size barrel. When you burn 53 to 60 grains of relatively slow burning powder, you generate a lot of hot gas ready, willing, and able to push the bullet to a high muzzle velocity, you need to give it room to work and that's what happens as the gas pushes the bullet up the length of the barrel. A .30-06 would see increasing muzzle velocity from a barrel as long as 45"; while that's not practical for a host of reasons, don't cheat yourself of a real ballistic advantage by cutting the barrel off too short - they don't grow back.
When picking a barrel contour, weight is your friend. Yes, the .30-06 generates more recoil than a .308, that's just basic physics; shoot the same bullet at a higher MV with more powder and you get more recoil. If you shoot a heavier bullet, as you should, then you get even more recoil. Now, this additional recoil isn't objectionable, even a tired old desk jockey with a bum shoulder (yours truly) can handle it, but a heavy barrel is one of the ways to make it reasonably comfortable. Normally I use the MTU/AMU profile that all the makers offer (Krieger #9), although I have a couple of heavy Palma barrels (Krieger #14) that work out well also - 6.5 lb. of barrel weight is your friend.
You might think that after 106 years there wouldn't be much to say about chambering a .30-06; actually, that's not entirely true, there are some fine points to consider. The first question to ask your gunsmith is whether he has a print for his .30-06 reamer; you really don't want to build a match rifle around an old hunting style .30-06 chamber of unknown dimensions. Even a lot of the old "match .30-06" reamers aren't a good idea because many of them had a 3 degree leade angle which will hurt accuracy compared to the 1.5 degree leade angle used today. Your best bet is definitely to buy a reamer for your project and take good care of it. If you think that 200 gr. is the heaviest bullet you're likely to shoot on a regular basis, then the Pacific Tool & Gauge Serengeti reamer, print no. 9685 is really a great choice. PTG makes great reamers, and this design works very well with bullets from 155 gr. to 200 gr. thanks to the freebore length as well as the case's long neck that gives a lot of flexibility in bullet seating depth. It is also a very good match to Redding sizing dies, another a worthwhile consideration.
If your preference is for heavier bullets like the 210 gr. and 215 gr. models now offered by Berger and Sierra, then I would suggest asking PTG for 0.070" longer freebore. That will still allow you to use medium weight bullets as well as the heavier ones. At this point, you might as well get a 1:10" twist barrel just for a slight margin of safety with respect to bullet stability in cold temperatures. I think once you go past the 200 gr. bullets, you're out of the "normal zone" with the .30-06 and it becomes a specialized chambering as opposed to an "all-around" shooter which is the .30-06's great strength.
If you want to shoot 230 gr. or 240 gr. bullets, the best bet is to throat the barrel after chambering to place those bullets exactly where you want them in the case neck. That's a more specialized operation, of course, but you'll really be building a single bullet rifle with a very fast twist rate that's beyond our discussion today.
Neck diameter is standardized at 0.340" for the .30-06 and it's a good dimension for an accuracy rifle. Although I turn my case necks to 0.0125" thick, for a loaded round neck diameter of 0.333", I don't consider that to be excessive clearance. Due to their length and taper, .30-06 cases will only last about 11 full-length sizings before you begin to see signs of head separation; therefore, I'm not worried about the 0.007" neck clearance accelerating case neck cracking (which would take at least 20 loadings), and it doesn't hurt accuracy. If you're sure you'll be turning necks, you can go smaller; but consider that unturned Lapua brass will yield a loaded round with a neck diameter between 0.337" and 0.338". That's as tight a clearance as I'm comfortable seeing on unturned brass; the 0.340" chamber neck is an all-around good choice.
In Part 2 we'll discuss brass, bullets and powder for .30-06 match loads. If there's room we'll talk about some tools and tidbits, if not then there will be a Part 3.
|Pacific Tool & Gauge .30-06 Serengeti Reamer|