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Old 08-08-2006, 07:06   #279
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Re: Cause of KBs

Originally posted by English
The man who did the entirely sensible experiment of successively shortening a 10mm case to find out whether his .40S&W Glock would fire out of battery had it right but I donít think that is part of the KB problem. If the cartridge is far enough out of the chamber to be dangerous the striker will be blocked in all but very rare cases. In this category of rare events the cartridge would be ignited before it is properly supported and the result would be a burst cartridge case not a burst barrel because the case would burst long before the pressure reached a level which would endanger the barrel. There has been no evidence put forward of any such mechanical failure of the striker safety block being the source of a case blow out.


The barrel and slide start moving back together as soon as the bullet starts moving forwards. Under normal circumstances the barrel does not cam down out of breech lockup until the bullet has cleared the barrel and the gas pressure is virtually zero. This obviously happens very rapidly and the empty cases of my G20 10mm show a smear of the firing pin indentation on the primer so the barrel is camming down before the striker has rebounded.


I believe that case blowouts are much more likely to be caused in this way than by a failure to go into battery combined with a failure of the striker safety block. If I were a proper engineer I suspect that I could do calculations based on the pressure resistance of the exposed case and the limitations on bullet velocity that would be created to show that this was so.

You mention an out of battery condition and claim that the little extra bit of exposed case shouldn't be enough to cause a blow out. However, you must also consider the fact that in this condition the gun is unlocked or partially unlocked, and therefore is likely to be completely unlocked before such time that the pressures have dropped to a safe level.

"the barrel is camming down before the striker has rebounded"

I don't believe the striker of a GLOCK rebounds as it does in most autos and remains forward until partially cocked by the action.
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