Had the opportunity to try out my newly refurbished upper from Kurt's Kustom. It functioned flawlessly through 200 rounds of 55gr Federal AE. When I go home to clean it, I removed the bolt/carrier and had to pry the firing pin retainer pin out with a small screwdriver. Both of the prongs were bent at about a 30 degree angle. As this part is cheap and easily replaced, I will just install a new one. However, what casued it to bend in the first place is a mystery to me and I hope it is not a sign of other problems.
Has anyone ever seen this happen before? Is it caused by excessive pressure?
The rifle is a Bushmaster and has all BM parts, including the bolt and carrier. Kurt modified my 14" HBAR with AK brake to an M4 profile with one of his A3 brakes. Also, the last round locked the bolt back every time but when the casing from the last round was ejected, it ejected weakly. Almost like it just fell out at my feet.
Any thoughts would be helpful.
As you said, the pins are cheap, and should be bought by the hand full.
To slow down the bending, it helps to aline the seam with the firing pin contact. This seems to slow down the possess, but will not stop the bending completely.
Also, due to the firing pin not using a return spring, the firing pin does come crashing back on the pin on the cocking recoil, and will cause it to bend over time.
The retaining pin is a wear item, don't worry about replacing it every few thousand rounds.
As for the weak ejection, use a little more CLP until the rifle breaks in, then back off to just keep the upper a little damp.
Hope this helps.
Just to let you know, that pin is supposed to have a spread in them so they don't easily fall out of the carrier.
The spread makes tension in the hole so if the bolt carrier is turned or dropped while doing a field stripping in the bush it won't just fall out and be lost rendering your rifle unless and making you combat ineffective.