by Hoot » Wed Mar 15, 2017 8:39 pm
With the additional weight and more importantly, shorter length (.920) start out with 34gr of IMR4227. The efficiency goes up as I expected with the additional weight. Work up in half grain increments and if QL is on the money, you should come into the sweet zone at 36gr or possibly a little higher. I have long ago gotten over the pain of pulling down loads and tossing the bullets though I don't strive for that. If I were approaching that experiment, I'd probably load up to 37 on the first iteration and watch for pressure signs as I walk the load up at the range.
Now for the bad news. I went back and reread your introduction post in the new members thread. The stock Bushmaster upper uses a carbine length gas system. It's not going to like slow heavy bullets creeping down the barrel. It may try to initiate the gas cycling action before they clear the muzzle and allow the pressure to drop, releasing the case from the chamber. Big, slow moving bullets were what led to the Corvette mod, to increase the bore dwell time. Watch for head swipes and distressed rims if you choose to shoot those heavyweights. That will be a sign that you should be moving to lighter, faster moving bullets and abandoning the juggernauts. IIRC, the dwell issue when using heavy bullets was more pronounced when running the 20" stock Bushmaster upper as it still used the same carbine length system and the bullets needed to travel 4 inches further before they broke the seal at the muzzle. I'm recounting this from memory, so take it as a best recollection. Others more familiar with the subject may wade in with reports from actual experience. I'm more of a lighter, faster guy in this caliber.
Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.