I converted a M1919A4 to 8mm swede (8X63) a couple years ago, and the results of the standard reamer were not good for the gun. It resulted in many hard extractions where the rim would be torn off the case. I ran an empty casing with valve lapping compound on it through the chamber with a drill until a slop similar to that found in the 308 or 30-06 barrels was achieved. I followed that up by polishing the chamber with a dremel buffing head and some rouge.

It worked great, and a mere 10,000+ rounds later I am now in need of another barrel as I have managed to burn this one out. And that was in semi automatic (although usually as fast as the trigger could be pulled).