I have a 243 on a commercial mauser action with 1/10 twist. Back when I shot a lot of 100 gr Hornady's, it really liked a full case of 4831, (the old 4831) Actually didn't even have to weigh it, just fill it full to the brim and compress it with the bullet. But now I generally only shoot 75 gr bullets in it and full pressure loads don't seem to be as accurate as about mid level pressure loads. Probably has something to do the overstabilizing the lighter bullets, etc. or harmonics in the barrel. What ever powder I use, it likes the velocity with the 75's to be in the 3250 to 3350 range. It has a light weight barrel on it. I haven't shot my 223 ultra handi enough yet to tell what it is going to like, am still breaking in the barrel. Anyone have pet loads with the 223 and 55 gr. bullets. I am hoping the 223 will shoot some of the commercial stuff accurately enough as I can buy it as cheap as I can reload.