I brushed a tumbler shaft hole with mild steel several years ago I drilled the hole out, may have used an end mill, can't remember. I turned the bushing on the lathe a little larger that the hole, again I can't remember how much. I then put the bushing in the freezer installed and let it warmup then reamed the hole to fit the shaft. Worked fine,for me, later sold the riflsvthat had the lock. Never heard of a problem with it.
Dennis