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Old 08-08-2006, 10:50   #280
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Join Date: Dec 2005
Location: London
Posts: 6,086
Re: Re: Cause of KBs

Originally posted by BuckyP
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.
If I remember correctly, you have missed a large and important part between the second and third parragraphs of mine that you quote.

Last part first - I think you are right about the striker smear. Thank you.

If, as you are suggesting in your first paragraph, the gun can be fired while slightly out of battery then it might well be that it could come far enough out of battery for the pressure to burst the case before the bullet leaves the barrel. If this was so we would see a smiley further forward on the remains of the case and a hole in the case at the rear six O'clock position. I am not denying this but have seen no evidence of it. In Walter G's terminology this would not be a KB since there is no overpressure and burst chamber, ringed barrel and so on.

It makes more sense to me to think of the whole range of proper KBs as variations on the same theme. They all show signs of excess pressure and not all can be put down to overcharging or undercharging. In some cases we have the remains of the case seized into the barrel so tightly that it can only be hammered out. The head of the case seems invariably to be blown into the distance. The front of the case can be seized in the barrel by only one mechanism. The pressure has to not only expand the case to fit the chamber but to expand the chamber itself to such an extent that when the pressure is released the chamber shrinks back onto the case, which had expanded to the swollen size of the chamber. It forms a compression fit which is used in some advanced mechanical assembly processes with high pressure hydraulics. In this case the pressure is not quite enough to burrst the chamber but is far higher than normal.

Since many KBs have not involved reloads it seems that the most likely mechanism is a partial and temporary blockage in the barrel. This delays the bullet long enough for the pressure to build to very high levels. That increases the temperature. That accelerates the burn rate of the propellant. That puts up the pressure, and so on to KB. If the bullet did not move there would be no recoil to open the slide and the chamber would burst. If there is a little movement the slide will start to move but the barrel will burst before it opens the breach. With more bullet movement there is likely to be enough recoil to open the slide before the bullet leaves the barrel and we get a simple burst case or a burst case seized into the chamber.

Since we don't find the delayed bullet in the barrel it does not form a complete blockage but since the pressures are enough to expand the bore, the bullet would be blown out past the obstruction anyway.

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