Rem 6 1/2 7 1/2 Primer Confusion

In loading for my 454Casull, it calls for a SRM primer. In this case, it would seem that a magnum primer would be preferrable. I'm wondering what the difference being Remington 6.5 and 7.5 are. Both are labled small rifle primers but on the 7.5 packet, it says Benchrest. I would think one would say magnum. Anyone know for sure? If so, which?

7-1/2 are br primers they are the same as the other just one is more consistent.
i doubt you need a magnum for such a compact case.
unless you are using h-110 in the cold. [30* or below].