Back in the 1950's when high quality match bullets were finally available, folks shooting the .300 H&H in competition at the longer ranges got best accuracy doing the following:
Handload new cases sorted to 1 grain spread in weight, no prepping of any kind needed, 69 to 70 grains of IMR4350 (2/10ths grain spread) with 180-gr. bullets or 66 to 67 grains with 200-gr. bullets, seat bullets out to just touch the lands. Sub MOA accuracy at 1000 yards was easily attained with a properly built rifle. Sometimes new cases need to be resized to uniform the neck dimensions.
Reloading fired cases, full length size fired cases in a die without an expander ball but its neck diameter about .002" smaller than a loaded round's neck, use a die that sized the case body all the way to the belt (Innovative Technologies - Reloading Equipment
), set fired case shoulders back about .002", same powder and bullet data. Same accuracy as with new cases.
Regarding case prepping and powders.........
As long as neck wall thickness spread's less than .001", turning necks ain't needed.
Case length can vary .005" and it doesn't matter as far as accuracy goes.
Nothing need be done to primer pockets nor flash holes. Your choice of primer makes a bigger difference than prepping the back end of the case. Wolf/Tula large rifle primers seem to be excellent these days.
Many folks tried 4831 but it never produced quite as good of accuracy as 4350. Yes, 4831 puts bullets out a bit faster with the same peak pressure but the bullets didn't land on target as close together as what 4350 did.