Are MG chambers bigger than other guns of

the same caliber??? I know that extraction was a problem with some, as the fluted chamber used by H & K and drip oilers used much earlier to lube incoming cartridges thus easing extraction will testify.......

I have a Jap M-99 that was once a dewat. In the course of making it a live gun, the weld removed from the chamber made it much too big.. I intend to rechamber it with a thread-in section. I was advised to get a reamer for 'Machine gun use'. The chamber reamers mfgrs tell me the std reamers will do just fine???

Any comment?? PJH

The chamber and headspace dimensions of (at least) US machine guns are indeed a bit larger than a rifle in the same caliber. I doubt you will be able to find a chamber reamer for this purpose, especially for a WWII-vintage Japanese MG. I would use a standard reamer and not worry about it.

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).