have a model 37 with 2 barrels. original and one that needs fitting. it is about 1/6 of a turn from rotating into firing position. If I trim barrel face and shoulder the same amount until rotates to 0 degrees and check headspace . is this the method or am i missing something? used to have a factory directions but cannot seem to find.

Yep in theory. With the possible need to deepen the extractor cuts. But I have to say that 1/6 of a turn from reaching firing position seems like a lot. It is only a 1/4 turn from on to off. I would figure out exactly where the interfearance is before I started removing metal. Both barrels are threaded the same? (all 37's aren't).

worked like a charm. had to remove about .008 to .010 at breech end . was enough gap between front of reciever and barrel didn't have to remove any there. headspace ok.