ive been using cci 400's in my ar's since i started reloading - several bricks of them to date. thats their standard cup small rifle (non magnum) primer. when i first started using it i did a bolt slam test (live round, gun pointed downrange at the berm) and while i got small dimpling, even after repeated full bolt drops - i gave up after around 10 attempts when nothing went bang. its been a long while since i tested it so i forget the actual count.. but it was somewhere about 10 attempts. i was also checking bullet movement - both setback or moving out - at the same time.
im sure there's a point where the cci 400 small rifle primer will slam fire, but i dont make a habit of chambering a round more than 4 or 5 times anyway (think hunting, where i'm loading/unloading a couple times a day during deer season) before i cycle it out and turn that round into a practice round anyway.
i think in this caliber - you're going to be more likely to get (excessive) bullet movement from repeated chambering than you will a slam fire with cci 400's.
i do use the rem 7½'s these days for my 450 loads, but thats because i have a bunch of them. i'm still using cci 400's in my 223 and 300 blackout loads since i have several bricks of them to burn thru and lots of load data with them from testing since 2011 when i first started using them as my initial reloading testing primer.
now... if you want to verify my results i would strongly encourage it - just take yourself to the range, point your gun in a safe direction and do a full bolt drop cycle. take your calipers to watch for bullet movement so you dont get into a dangerous thing there, and watch the primer hits as well as OAL changes. you might be surprised what you learn
HTH