Smaller area of the small primer leaves more supporting brass in the case as well.
I run the 450 CCI and other than one bad lot, have never had an issue. I've fired 5000 or so rounds out of my 6.5X47 Lapua's.
I tend to run the lighter bullets. Mostly the 123 MK's and A-Max's.Getting 2975 or so out of a 25" 8 twist Rock.
The 129 SST's I hunt with get right at 2900.
I do not hot rod as I need the rifle to function both in matches and hunting.