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Is Glock the only pistol that comes w/an unsupported barrel,and whats the advantage.
Glock isn't the only one, nearly everyone does it to a degree, and it usually is a non-issue. However, Glock relieves more of the chamber than most, and got famous for it, and it has caused issues in certain cases.
Why do they do it? What's the advantage?? Feeding reliability.
Essentially, what the gun is doing is trying to shove a straight cylinder, or very slightly tapered cylinder, with a dull point (or no point) into a steel hole that is only a couple thousandths of an inch larger than the cartridge, doing it very fast, and from a slight angle. Making the chamber bigger at the back (removing more metal, on the bottom of the chamber) means the cartridge has a bigger hole (taller) to enter, which means it has more "room to make the turn" in order to be lined up with the bore to enter the chamber all the way.
As stated, the solid brass head of the case doesn't need the support of the barrel. It is strong enough to handle the pressure, so cases don't need to be supported all the way to the extractor groove. Regular barrels support the case down to the solid head of the case (which begins a short distance above the extractor groove).
Glock, and some few others have chambers where the support ends a short distance ABOVE the solid head, leaving a portion of the thin case wall
unsupported.
This means more room (clearance) for the round to enter, and means they feed more reliably. BUT, there's no free lunch. The unsupported case wall stretches under the pressure of firing, It BULGES out. This is not normally a problem when firing a case ONCE.
Glock doesn't care if the case bulges, from their point of view, it only has to work once. There are a number of firearms that are not "reloader friendly" the way they treat the brass. Most are designs intended for military use. Doesn't matter what happens to the case, bulge, stretch, get banged up or even ripped rims as long as it doesn't rupture in the chamber, and gets cleanly ejected after firing.
The problem is that when the stars line up, you get a situation where the brass doesn't just bulge where the thin wall is unsupported, it ruptures. This releases the chamber pressure back at you. KA-BOOM!!
Brand A ammo fired in an unsupported chamber may be perfect fine (once) bulging, but maintaining its containment of chamber pressure. Brand B might have a slightly thinner case wall (and still be in spec) so that when it bulges, its not quite as strong (at the bulge) as brand A, and so Brand B tears open (ruptures). And, both brand A and brand B can work fine in a gun that does not have its chamber relieved as much as Glock does.
Glock became famous for this happening with their early production runs of .40S&W. Apparently what ever ammo they used during their design testing was "Stronger" than some of the ammo commercially made and sold to the US public, so there were a number of blowouts.
Something did get changed, and I don't know if it was the ammo makers increasing case wall thickness, or GLock deciding that their "perfection" needed to be "adjusted" but the Ka-Boom problem has gone away, pretty much (with factory ammo, anyway
) but the memory of it, lingers still...