When loading .308W for use in my AR-10, should I be keeping loads in the Service Rifle zone, or are hunting loads acceptable? I've just loaded mixed year Lake City brass with CCI LRPs, Hornady 150 gr BT-FMJs, in 0.2 grain increments to the powder range in the Hornady manual (max = 44.9 gr) for that bullet.
Yet Hodgdon, Nosler and Lyman all have Varget loads for 150 gr jacketed bullets up into the 46.5C and 47.0C level (2900 fps vs 2700 for the Hornady load).
Should I be reserving the higher pressure and velocity loads for my bolt action?
Lyman, but no other source, mentions that I should keep loads 1 to 2 grains lower than max if using mil spec brass. And I did see at the 44.9 gr load, the case looks to be full to just under the neck. This might be a compressed load if the bullet is seated to the cannelure.
If you want to have rounds that feed and extract you are better off using "service rifle" loads.
Firstly, does what does more mean? What do you really get with the extra velocity, besides, extra velocity? Everything you read in print pushes increases in velocity, but they don't show any differences in wound channels. The comparisons are always in kinetic energy, a bogus measurement of lethality in my opinion, and bullet drop at over the horizon distances. Distances which are unethical, unlikely to encounter in most of the US, and beyond the marksmanship capability of most of humanity. But lets say, out to 300 yards, the drop on a 2700 versus 2900 fps bullet is going to be within your hold, and at 2700 fps the bullet will expand predictably at that distance.
I don't have an AR10, I have Garands, M1a's, PTR 91, and FAL's. I did not use Varget powder, tested it once in a match M1a and came to the conclusion it was a bit slow for the gas system. It caused case separations. I am going to recommend the any of the 4895 powders. That is, IMR 4895, H4895 and AA2495. Accurate Arms told me they blended AA2495 to the IMR 4895 pressure curve, and I shot kegs of the stuff in competition, and it shot very well. The 7.62 cartridge was developed with IMR 4895 powder so, in my opinion, it is first choice for gas guns chambered in 308 Win. I also like IMR 3031 because it is now short cut, and a little faster than IMR 4895. I want a powder that has a quick pressure drop, which increases the chance the case is not stuck to the chamber on extraction.
Based on my testing of 150 Hornady FMJ's, I would start with 42.5 grs IMR/H/4895 and stop at 43.5 grains. Looking at my data, 41.0 grains IMR 3031 worked well. (my notes say "outstanding accuracy")
You can experiment with higher powder charges, eventually you will find the powder charge level where your rifle rips the rim off of cartridges, sticking cases which require a cleaning rod to remove, and you will experience strange bolt over rides and cartridge jams in the magazine. You want these to occur at the range, where you have access to all your tools. I always carried a leatherman when shooting AR15's because clearing some loading port jams was impossible without needle nosed pliers. I also carried a cleaning rod inside the tube of my spotting scope, and I was very popular with those who had jams on the firing line.