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Old January 18, 2013, 08:11 PM   #15
James K
Join Date: March 17, 1999
Posts: 24,136
Back a bit to the firing pin stop. Many folks have heard of the firing pin stop dropping down and hanging up the gun, hence the concern to make it a tight fit. There is no harm in doing this, by peening it but some understanding as to how the firing pin stop could drop down might help.

When the hammer hits the firing pin, the firing pin moves forward far enough to strike the primer. But it cannot normally move far enough to clear the firing pin stop and the slide movement to the rear cocks the hammer in the normal manner, just like in the pictures.

But, with hot ammunition, and some gun characteristics like an extended ejector, the fired case is kicked away from the breech face before the firing pin loses inertia, so it continues to move forward. That pulls the rear of the firing pin out of the firing pin stop.

Now in the pictures, it looks like the slide moves gently back and pushes the hammer so the hammer stays in contact with the FP stop and it can't move down. But that is not what happens with hot loads. The slide moves back so fast and hard that it strikes the hammer, driving it back and down out of contact with the slide. So, with everything just right (or wrong) the firing pin is clear of the slide stop and so is the hammer.

Meantime, the gun has begun to recoil upward. The firing pin stop, having nothing to hold it in place, tries to remain where it is as the gun moves upward. The firing pin stop thus moves down (in relation to the gun and slide) and ends up between the hammer and the frame, jamming the gun.

It is a neat case of timing, and won't happen except with hot loads. It won't happen with standard GI loads. But it happens often enough that "gurus" advise shooters to stake, peen or otherwise make sure that the firing pin stop won't move down and hang up the gun.

Jim K
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