You will be OK using magnum primers with W231, it is a very well behaved powder. Keep the loads down around Hodgdon start levels, which looking at Hodgdon's data for a similar weight bullet looks like 4.4gr. You shouldn't see any breech face erosion with those primers at that load level.
Hodgdon lists 3.9gr as the start load for a lead bullet of that weight, so if you wanted to be extra careful, you could start there and work up, maybe use the mid-4's as your max. 3.9gr may or may not cycle your gun so don't load a ton in that range to start.
Your load length also gives you a little extra margin.
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