About 5 years ago, I acquired 500 rounds of ammo from the AMU. Loaded with 75 grain A-Max, all were in IMI brass with some sort of ball powder that I think was probably 2520. The amazing thing about this ammo was that out of a 26” barrel, it made 3080 FPS average. Yes, out of a 5.56. It was loaded long, so was intended to be fired single loaded off of a sled, but this stuff was super accurate with many groups going under 1/2” wish I had a few thousand more of that, but alas, it’s all gone. I did figure how to duplicate it though. Same brass, Wolf SRMs primers, CFE-223 powder, and 80 grain Sierra MKs easily break 3000 FPS and shoot like a house afire out of my 26” Hawk Hill 7.5 twist barrel. I’ll not give the powder weight for fear some one might break an expensive rifle following my recipe, but you can work up from 23 grains in a strong bolt action while reading primer flattening and signs of stiff bolt lift. Till your satisfied that you’ve reached max. As always when discussing load data, your results may vary.
Wayne