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
By: Germán A. Salazar
That's a good question that deserves some thought, more people should ask.
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 However, like the Sierra 2155, it's an outdated design and not worth buying now.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.
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.