Dave:
I believe that Charlief1 and dynoman pretty much nailed the query for the difference between standard small pistol primers and small magnum primers.
I have bought Winchester large pistol primers from Powder Valley, which I believe is in Missouri or there about. I generally buy Aliant Bullseye powder from local gun stores but that is getting old and pricey, so I will probably buy a 4 or 8 lb keg from Powder Valley the next time around.
I buy Dardas .45 auto, 185 grain LSWC bullets direct from Dardas, not cheap, but I consider them the best of the companies that cast the 185 grain .45 cal bullet. The quality of their bullets is unmatched, amongst several companies that I have tried.