AR10 Mystery

[LawnMM]

Okay, so here's an interesting occurrence. I get home yesterday after a match, and when I pull the rifle out of the bag and lift it vertical I hear something rattling around inside the receiver. The receiver resists being opened, takes a bit of doing to get the halves to separate. Apparently the firing pin retainer is MIA. Where it went is the mystery. I find it hard to believe the rifle cycled properly, flawlessly actually, through around a 70 round day shooting without the retainer. I would think the pin would slip right out the back of the BCG under recoil without a retainer. Especially having carried the rifle vertically most of the day.

No damage to the gun, thankfully, other than a little burr on the firing pin I had to remove from where it jammed up the receiver when I pulled it out of the bag. That pin is captive when the BCG is in the gun, so how did it mysteriously find its way out of the gun? Could it have cycled all day without one? I'm having trouble seeing how that's possible, I'm wondering if my gun was being fondled when I wasn't watching.

Thoughts?

 

[Thumper580]

Is the pin laying on your bench when you cleaned the BCG?

 

[DavidAR10]

Tell us more of this Coke drink.

Is it kinda lemon-lime or orange?

EDIT - oops, forgot this guy:

BTW, as I asked but in different words than LRRPF52, what Coke drank is it?

 

[LRRPF52]

Could have broken on the last round. IS your rifle a DPMS pattern gun, or an Armalite?


The pin shaft could have ejected out of the ejection port, and the head fallen out through the mag well.
Armalite uses a spring-retained firing pin, so I'm guessing this is a DPMS BCG.

I have bent at least 3 DPMS firing pin retaining pins with my .260 Remington. Needs a smaller firing pin hole.

 

[LawnMM]

Is the pin laying on your bench when you cleaned the BCG?

That's what I was thinking, checked the bench and the whole room it sits in, no sign of it.

Could have broken on the last round. IS your rifle a DPMS pattern gun, or an Armalite?


The pin shaft could have ejected out of the ejection port, and the head fallen out through the mag well.
Armalite uses a spring-retained firing pin, so I'm guessing this is a DPMS BCG.

I have bent at least 3 DPMS firing pin retaining pins with my .260 Remington. Needs a smaller firing pin hole.

Its a DPMS pattern, built on a MATEN receiver set and JP BCG, I ordered some spares that I will keep in my tool kit that comes to the range/matches with me. Just kinda surprised the gun would function and not bind up without it present.

 

[ORD]

Just kinda surprised the gun would function and not bind up without it present.

Generally speaking...it should NOT function which leads me to believe that LRRPF52 is likely onto something when he suggests that it was most likely your "last round of the day" when the break occurred (or it occurred gradually until it finally all came unglued), however it managed to occur. FP retaining pins aren't the strongest parts in the world and they can break or otherwise get "misplaced" (cough, cough, cough) when you disassemble the BCG for maintenance, but honestly, I have yet to see one of the "solid" pins like JP uses for their .308 BCGs get broken which makes me also think it COULD BE something other than a broken part that led to its disappearance from your carrier.

 

[LawnMM]

To clarify, I removed the BCG prior to the match to lube it up a bit, never pulled the rifle out of the drag bag when I did it. If it were going to hop out of the BCG through fault of my own, I'd have expected it to land in the bag, or if it got a running start, on the floor in front of the bench where I lubed up the BCG. Like I said, it is still MIA, and had that been the case that means I went the whole day, upwards of 70+ rounds with no retainer and it didn't fubar the gun. I find that unlikely. I didn't open the gun up again till after I got home and pulled it out of the bag and heard the firing pin drop out of the BCG and start jingling around inside the receiver.

I'm at a bit of a loss. I've ordered replacements that are DPMS solid pins not the cotter pins so I guess its something I'll have to inspect more often to make sure that pin isn't failing. It may not be the strongest part in the gun but I can't believe there's a ton of stress on it either. The hammer should stop most of the initial spring back of the pin after the primer ignites. At that point it just needs to keep the pin from falling out of the BCG as the BCG cycles.

It was an odd occurrence. For sure.

 

[ORD]

To clarify, I removed the BCG prior to the match to lube it up a bit, never pulled the rifle out of the drag bag when I did it. If it were going to hop out of the BCG through fault of my own, I'd have expected it to land in the bag, or if it got a running start, on the floor in front of the bench where I lubed up the BCG. Like I said, it is still MIA, and had that been the case that means I went the whole day, upwards of 70+ rounds with no retainer and it didn't fubar the gun. I find that unlikely. I didn't open the gun up again till after I got home and pulled it out of the bag and heard the firing pin drop out of the BCG and start jingling around inside the receiver.

I'm at a bit of a loss. I've ordered replacements that are DPMS solid pins not the cotter pins so I guess its something I'll have to inspect more often to make sure that pin isn't failing. It may not be the strongest part in the gun but I can't believe there's a ton of stress on it either. The hammer should stop most of the initial spring back of the pin after the primer ignites. At that point it just needs to keep the pin from falling out of the BCG as the BCG cycles.

It was an odd occurrence. For sure.

My "cough, cough, cough" was directed at my own stupid goofs over the years with various AR platform rifles and parts/pieces/@#$% going missing on me in the middle of a quick clean/lube between rounds or just otherwise vanishing without a trace on the range. Stuff happens...not saying that was what happened in your case at all. Hopefully your suspicions re: someone monkeying with your kit while you weren't looking prove to be untrue...hate like hell to think about any fellow shooters would do that, but the world's full of all manner of @#$%ing jackasses these days so who knows.

 

[TallShot]

That's pretty wild.

I'd love to know what happened as well.

 

[TallShot]

That's pretty wild.

I'd love to know what happened as well.

 

[AXEMAN]

cotter key style pin or solid pin? by the way, I got 3 solid pins off ebay for $7 shipped.

 

[LawnMM]

Solid pin

 

[AXEMAN]

I don't see how it could come out easily. there isn't much space, not enough inside the upper for it to be slid out in either direction with the bolt inserted. even if the head sheared off. mine I had to tap in, could yours have slid out without you using a punch? was its fit tight or was it a loose fit? it would seem it would have had to have come out while you had the bolt out at some point. the retaining pin may have come out and the firing pin just slid back thru the carrier to rest on the buffer while vertical. that being said its hard to imagine weapon firing when you went to shoot as the rifle would have to be tilted down to let the firing pin fall thru the carrier. and its hard to imagine the pin just flopping around in there for that 70 round string like you said. I wouldn't even want to duplicate the event because all I see is a firing pin getting munched up. pretty weird

 

[LawnMM]

Extremely weird. The pin was a loose fit, as are the replacements. If the head sheared off the pin could work itself out the ejection port side of the carrier. With less than 150rds through the gun and no real stress on the pin I don't see how that's possible. Also as you said, had it been loose and flopping all day I'd have heard it, like I did immediately after pulling it out of the bag at home.

It won't come out without pulling the bcg out of the gun...

 

[AXEMAN]

gremlins. yep, gremlins


VERY FUNNY!! Bugs Bunny vs a Gremlin. - YouTube

 

[tipper]

This is one hell of a tell