[T. O'Heir]

21.6 grains of BLC-2 is way below current minimum for a 60 grain bullet. Elderly manual?
"...not removing the crimp leak gasses..." Like Nick says, the primer pocket will be a tick out of round with a tiny bit of brass in the wrong place. Lets gasses escape.
Magnum primers are about the powders used and nothing else. They're for lighting hard to ignite powders and extreme cold weather shooting. They burn a bit hotter for a bit longer than regular primers. BlC2 doesn't need' em.
Isn't going to bother anything if you do use 'em though. Pressures might be a bit higher, but not enough to hurt anything.
7 1/2 primers are small rifle bench rest primers. Federal 205M's are Small Rifle match primers too. Never seen any difference using match primers myself.
"...really is so much to learn..." Read your manual. Read the reference chapters too.