Originally Posted by dm1906
The rounds, when chambered, are firm against the breech, held by the extractor. If it didn't do this, the .40's wouldn't fire. The Glock slide is the "bolt", one piece.
There are headspace tolerance considerations. There is far more play in the gap of the extractor holding the rim than there is in the chamber holding the cartridge MOUTH. That is equivalent to much greater headspace variation, even if the .40 round DOES fire consistently. Field strip a Glock, place a case in the extractor, and wiggle it fore and aft. THAT amount of wiggle is now the headspace variation. Would you tolerate that much headspace variation when shooting 10mm in a 10mm factory barrel?
"Getting along" with shooting .40 in a 10mm barrel is something I did (before scrounging conversion barrels), but I never contend it is an equivalent condition to shooting 10mm cartridges.