Yes, it has to do with the bullet, bullet ogive distance, powder used, and the pressure it generates at the right time. They also load on the lower accuracy node (lower speed), which is easier to tune. When you get up into the higher pressure and speeds, this accuracy window is smaller. The 168 SMK is one of the least finicky bullets to load for. When you get more aggressive with the design, like a higher BC bullet, more aggressive ogive, and different boat tail design, the bullet does become more difficult to have a large accuracy node in all rifles. But their powder charges do have some large swings which is why FGMM often has a high extreme spread from round to round to round.
I have also been working on powders, pressures, bullet ogive's, and researching this. I think I've also found some great loads with a slightly slower burning powder to get the speeds up and shoot really well in 5 308's that I have shot them in.