I'm no expert on the subject but a couple of things I have noticed is neck tension and bullet design. I think seating depths and pressure(s) also play a role but don't know enough yet.
Specific neck tension is a new "learning curve" for me. All I ever really knew was that it needed to be consistent throughout the lot of brass I was using and that was controlled by regular annealings and sorting your brass. With consumer annealing machines becoming more affordable & available, hopefully the science will soon be common knowledge. You can find your rifles preferred tension by using bushing dies and purchasing different internal diameter bushings. If you got multiple rifles/cartridges it can get expensive.
By sorting brass I mean keeping it separated by the number of times it's been shot and by head-stamp, if you use different mfg's. The work hardened condition determines its softness or brittleness.
Bullet design: I've noticed a trend in about three of my rifles. In my .300WinMag (Pac-Nor), I can shoot Berger 215gn Hybrids and 212gn ELD-X's with the same load data and the ELD-X's slightly beat out of the Bergers in accuracy, velocity and ES/SD's! It's not much but I see it on the LabRadar and on paper. I first noticed this when shooting 140gn VLD's and A-max's in my 6.5-284Norma (Lothar Walther). Again, recently in my 6mmBR (Shilen), the 108gn ELD-M's are just a tad tighter and consistent than Bergers of similar weights. I don't know why. Truthfully, I really want the Bergers to shoot but I can't kick the Hornady's to the curve, especially if I feel they'll give me a edge at LR, PLUS they're CHEAPER!