Need advice, bad cotter pin

[Trinket]

Please forgive my ignorance.
A very generous man bought my daughter the upper for an M4 and she built the rifle from the ground up under his supervision. It's her "baby."

The problem is this, after we shot it and we took it apart to clean it we found that the firing pin cotter pin was spread too far apart and it was a bear to try to get back in when we put it back together.

Circumstances changed and I don't know if I'll see this man again and he was our expert in these things, so I'm completely lost. Do I call DelTon where he bought the M4 upper from and tell them what part I need since it obviously came to us new that way? Or, is there just some generic place we can purchase a firing pin cotter pin in the Bay Area for an M4?

Thanks for your help. My daughter is eager to practice disassembling and assembling her "baby."

[m1aowner]

Looks like you need part#14. I like Brownells. I always use them for little nick nack parts.

http://www.brownells.com/.aspx/pid=0/sid=811/schematicsdetail/Bolt___Carrier_Assembly

[Trinket]

Hey, thank you. At least it's cheap!
Thanks again, much!

[mjsweims]

Not sure about guns, but in my line of work we do not reuse cotters. Bending, then rebending them cold works them, and this is even more of a concern the smaller the size.

[rabagley]

Not sure about guns, but in my line of work we do not reuse cotters. Bending, then rebending them cold works them, and this is even more of a concern the smaller the size.

This cotter pin that retains the firing pin in the AR bolt carrier is not bent after insertion, so it doesn't suffer from "reuse" just because of a bolt carrier teardown, cleaning, and reassembly. Any pin with one end enlarged would work as well (and you can buy a more expensive machined mushroom pin to use instead of the small cotter pin that everyone else uses).

[jester]

Try this;

http://www.knsprecisioninc.com/mm5/merchant.mvc?Screen=PROD&Store_Code=KNS1&Product_Code=PERMA&Category_Code=AR15GP

Got 1 in both my builds.
Easier to remove & install than a cotter pin

[CrippledPidgeon]

The problem is this, after we shot it and we took it apart to clean it we found that the firing pin cotter pin was spread too far apart and it was a bear to try to get back in when we put it back together.

It's not REALLY a cotter pin, and it should be slightly spread at the legs. It's better to have a tight retaining pin than a loose one. I would say that unless you're trying to learn how to reassemble your gun with your eyes closed, don't worry too much about it.

Or, is there just some generic place we can purchase a firing pin cotter pin in the Bay Area for an M4?

Brownells should have one, and it's a very generic piece. Probably best to order some tools or something to make the shipping worthwhile.

[Trinket]

Thanks so much for the great ideas everyone.

[Army]

Yep, should be rather snugly in there. The guy actually did you a favor.

[trautert]

As someone mentioned, though, look for a few other items to put in your shopping cart, or your shipping charge will be grossly larger than your purchase.

Don't as how I know, but check the price on a bolt catch roll pin.

[five.five-six]

once the BCG is in the upper, the retainer can't come out, it's held in place by the upper, all that pin does is keep the FP from flinging out the back of the bolt. you could use a toothpick in a pinch

[Trinket]

I knew I could count on everyone for help. Thank you so much for taking the time to help us like you have. You're awesome!

[johnthomas]

Stick with calguns, these guys are awesome. Your daughter will be impressed with everything you will learn, lol.