I work at a gun shop and a guy brought us his 300 ultra mag and said that he couldnt make it group and wanted us to develop a good handload.(remington is all that was available for it) Well there wasnt much reloading data at the time for the UM so we took the bullets out of a few factory rounds to get an idea of how much powder they were using. The first 2 rounds that we took apart varied by 4 grains of powder. we took 10 shells apart with as much as 6 grains variance in them. We just average the powder out and put the factory bullet back in and had groups under an inch.
I will never shoot remington ammo again. Only winchester for me.