Re: Bumping shoulders
Personally, I would prefer that bumping was never needed but itís not like there is any choice there. Eventually itís needed.
I donít think bumping is difficult with better cartridge designs, normal pressure loads, well matched dies, suitable press, and consistent application of a good lube. But accurate bumping can get difficult quick for reloaders who depart from these conditions.
I ran into an ugly sizing/bumping issue once in 6XC with one of Tubbís ĎFerrari of diesí, that was seriously mismatching with my T2K chamber(way over sizing). I had JLC Precision make me a bushing/bump die for it, problem solved.
Oversizing the body can result in inconsistent headspacing, to negative headspacing(opposite of bumping). With this, lower body brass is rolled up into the shoulder, countering any bump action. Further sizing still rolls this forward pushed shoulder brass up into necks, increasing donut, tension, & trim length, while still leaving bad headspacing.
Anything can be taken too far..