I have been using REM 7 1/2's ever since I bought One of the first .17 cal Rem Model 700's rifles.
They were made for the .17 Rem because of the pressure. As far as 6 1/2's I never liked em even in 222 because I drove em harder than factory.
I considered 6 1/2's junk primers

I still Use 7 1/2's in .17, & 223 if loaded to 5.56 pressure because if you use the same hot loads in either caliber with most any other primers they flatten or end up pierced, & eats away at your firing pin.

. I remember back in the day{70's} Ad's from Remington showing a longer duration flame front, not hotter burning just longer lasting
compared to to other primers, that picture clearly showed the flame front while other primers were already done. That + the much harder Bronze cup.

I still have a bunch of the Rem 7 1/2's, all saying BR, or Benchrest. I don't waste these just to burn up ammo, they special. LOL.

I would have got him too but a Dad Blam snow flake hit me in da eye....