Its happend to my 7-30 waters, 375 jdj, 45-70 factory barrels. I purchased a head space dial indicator, and found the brass sits .006 to .009 from being flush on the barrel. My custom barrels sit flush 0 with no miss fires. I my researching the problem I find proper head space is .006 and under. my barrel to frame is .003 with .006 case inside the barrel .009 total head to frame head space and higher. I'm guessing this may be the problem.