I think that the chamber geometry of the 270WSM may have something to do with the lower velocities (no throat). When I got mine years ago I was blowing primers trying to exceed 270Win velocities 150 grain bullet. I even had it throated and still only got a little over 270Win velocities. Hodgdon only lists 3070fps with Retumbo so slower powder doesn't seem to be the answer. Haven't played with the WSM in a while though. Western does show 3100fps with Magnum but never tried that.

My 270Win gets 2950 with Magnum and shoots the 150 NPT just under 1", so see no need for WSM.

Ed

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