RE: Primers
I would pick federal 215M. And also pick up some Winchester large rifle mags. You would like to have two different primers. I have seen a few times where changin primers made a world of difference. Not always but sometimes.
Not sure for a 7.5?
Mainly it depends on your powder. For instance, with 300RUM, I used 215M or CCI250, and even tried rem 9.5Mfor anything slower than RL22, but had great luck with 150gr bullets and 210M in it with faster powder like 4350.
I would start loading RL22 or IMR4831 for the 300win.