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Posted: 5/29/2005 1:42:21 PM EDT
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I have a DPMS AP4 with about 7000 rounds through it. Today, every second (third and forth) round wouldn't fire. I check the firing pin and it appears as though its now sitting to far back inside the bolt compared to when it was new. As I recall, the rear part of the firing pin had a small circular flat with bevelled shoulders. The shoulders sloped down to meet the back of the bolt flush. In other words, you could not see any of the cyllinderical part of the firing pin, just the smalll flat and the shoulders. Can somebody check their bolt and verify this for me. Now my firing pin appears to extend about .075" further out from the back of the bolt so now you can actually see the cylinder part of the firing pin and I think this is why its not firing. The distance from the front of the pin to the bolt face is now longer and the hammer isn't able to send it far enough forward to properly impact the .22 rim. I took it apart and the firing pin is made up of two pieces. It appears there is some wear, where the two pieces meet. This may be the problem area but since I don't have a new bolt to compare, I'm kind of stuck. Any help would be appreciated. John |
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I'd start by asking DPMS if I were you. I've got one of the DPMS M-4 .22 uppers and have had a few problems with failures to fire on some ammo. I contacted the factory and they were quick to respond. (They recommended changing my hammer spring and trying other ammo - CCI Blazer and/or Federal American Eagle. A new hammer spring helped, but I haven't found that ammo locally yet - the more reliable brands I have tried are approximately 1 failure to fire in ~20rds. DPMS noted that some Remington ammo did not work as well due to hard primmers). A friend of mine has a DPMS upper that is reliable. In our effort to trouble shoot my problems (after I changed the hammer spring), we compared the firing pins. We noticed the following: - his firing pin was slightly longer (1.686" vs only 1.678") - my firing pin has a slight taper (at the inside base), while his was almost flat. - when the firing pin was pushed to the forwardmost position, his protruded almost to the bolt face while mine was set back slightly more. I just checked the rear portion of the firing pin that protrudes from the bolt (that you noted). On mine, I can see the side of the cylindrical portion of the firing pin. I didn't remember that the firing pin was in two pieces, but I could be mistaken. (I don't remember and don't have a punch set to easily dissasemble my bolt). Good luck. Let me know what you find (my problems may be related). Martin |
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