I've made primer pocket reaming part of my standard prep for new brass. I've been using more Norma and Nosler brass in the last few years and these brands seem to have issues when trying to seat primers deep enough. This may also be due to my use of Federal LR primers which are .0005 larger in diameter than other brands IIRC.
Dunno about that statement concerning Federal primers.
I'd heard all sorts of things about primer dimensions over the years, and a few years ago decided to measure a bunch to see what was up. Could find NO consistent difference in large rifle and small rifle primers of various American brands--and in some instances different manufacturing lots of the same brand averaged smaller or larger in diameter.
Measured 11 brands/types of Federal, Remington and Winchester Large Rifle primers, with a digital Starrett micrometer, all that the same temperature. One lot of Federal 215s was the largest in diameter--but Federal 210 and 215 Match primers were on the small end of the diameter-spread. Only had one kind of Federal Small Rifle primer was measured, the 205 Match--which ranked the second-smallest in diameter of the 10 primers. That info was published (along with a bunch of other info about modern rifle primers) in Chapter 3 of the first BIG BOOK OF GUN GACK.
I suspect the truth is that ALL primers vary somewhat in diameter, depending on the lot, due to the wear-use of the cup-forming dies.
