Its 17 years since I had a Rem 700 Classic in 7mmRM, and back then Reloader 22 wasn't available in Oz, and ADI hadn't made AR2225 (HRetumbo in US).
I found that the 2 standout powders with the 175 grain Sierra were IMR7828, and H870.
MY experience is that the burning rates of IMR 7828 and Re 22 are similar, but personally I believe HRetumbo has a burning rate that is much better suited to the 175 grain bullet than Re22, and will give a much better loading density as well. My chrono data from back then:
Rem cases, Fed 215 primer.
77.0 grains H870 - 2901
78.0 grains H870 - 2977 (Max)
65.0 grains IMR 7828 - 2,740
66.0 grains IMR 7828 - 2,808
67.0 grains IMR 7828 - 2,883 (Max)
I note on the Hodgdon website that they list 77.0 grains of H870 as maximum, but only list a velocity of 2,782 fps. Obviously a much slower lot than I was using. They list 77.0 grains of US 869 as producing 2,758, which in my opinion is a pretty low velocity for what is achievable in a 7mmRM.
I note that Hodgdon list 68.0 grains of HRetumbo as maximum and producing 2,800 fps, which again seems very conservative to me. Only last week when testing both AR2225, and H870 in my 257Weatheby with the 156 grain bullet, the maximum load for AR2225 was 65.0 grains, and 70.0 grains for H870. I noticed the same 5 gain differential between these 2 powders in my 25/06AI.
My suggestion is to start at 65.0 grains of HRetumbo and work up from there, and would be interested to hear what your maximum load turns out to be. Good luck, Brian.
