i shoot barrels from kkm precision,carson city nv.775-246-5444,discount for L.E. and MILITARY. all my barrels were drop-in no fitting required--g19,g23,g30 g29 g20 and g21, my g36 has a jarvis barrel(before i found kkm)
years ago i got a few cases of cci blazer-aluminum cased- 9mm real cheap,had some fail-to-extract with kkm g19 barrel so i used the stock barrel for the cci blazer(shot in idpa matches).never shot any more aluminum-cased ammmo.
i`m a reloader and other than the cci blazer i`ve never had a problem with kkm.