Its worth experimenting with the jump of the bullet to the rifling. If that dimension were to be something the rifle didn't like, all the other variables, powders, bullets, you introduce will likely seem meaningless. Kind of like trying to tune up your motor, with one plug unhooked. I've often found that rifles will favor a jump of .020" or less. If that makes an over all length too long for the magazine, I go to the length that fits, and start going shorter, in .005" steps. In a very accurate rifle, its not unusual to see the group shrink, then expand, as you cross the "sweet spot", and if you go in .010" steps, you could skip right over it. If you have other problems, like bad bedding, all the testing could look terrible, until the problem is corrected. One I fooled with drove me crazy. Nothing helped. Finally, I gave up on the bullet I was trying to get to shoot, and went to different one. Shortly after that, it displayed a two group pattern: it needed to be bedded. After that was done, I looked at the notes from the first bullet, tried one that had showed some promise, and had a one holer.
