Sorry DF, was asking Mossyrock. Nice snag on the FN.
I mostly let the bottom metal be my guide as well, but do chop without any consternation...of course, my smitty is no hack...:)
Better to be satisfied with the choice than enduring the cognitive dissonance involved with cartridge remorse later...and action-wise for me, there is no substitute for fine old mausers...
FWIW, my advice to the OP is to do the action purchase justice by taking enough time in making sure of your cartridge selection decision, rather than worry about doing a little smithing on a commercial mauser action.
