AR 15 bolt carrier hitting buffer retainer pin

[ForceTA308]

*Edit*- Found my issue was due to my charging handle hitting an excessively thick buffer tube end plate. Replaced it and problem solved!

Tried searching around but couldn't find this issue.

I've had a complete Anderson lower for a while now and finally got around to getting an upper for it. Upper is PSA with PSA's "full auto" BCG. I'm not sure of the lower parts kit as it was already assembled when I purchased it.

My issue is that I'm having to pull the rear take down pin and lift the back of the upper receiver up slightly to get the BCG to the rear. Looking at it, I guess the carrier is hitting the retainer pin for the buffer.

I took the bolt out of my RRA and threw it in the PSA upper onto the Anderson lower and had same issue. Took PSA bolt and put it into my RRA and it cycle fine. Am I going to have to finesse this retainer pin a little until the bolt is able to cycle over it? I have some tolerance, maybe enough to get me where I need to be. Wanted to check it out with you guys before I started in on it.

Appreciate it as always INGO!

 

[Jeremy1066]

 

[jd4320t]

Are you sure your buffer tube is screwed in all the way holding the pin down properly?

 

[ForceTA308]

Yeah, I have a couple pictures I'm working on getting up. Yes, though, the buffer tube is seated over the pin. It's the spring loaded retainer that I think I'm hitting.

 

[ForceTA308]

 

[M67]

How tall is the part of the pin that holds the buffer?

 

[wsenefeld]

With the upper pinned to the lower, does the bcg move rearward at all? If it moves rearward about 1/4 of the way, the hammer may be getting stuck on the ramp of the bcg. Not saying it is the hammer but I'm trying to eliminate it as a culprit. Remove the hammer and see if it cycles?

This is the issue that my Palmetto PA-10 (.308) had.

 

[midget]

Easiest way to tell if it is the retainer is to remove it. It likely isn't that though. As stated above, it is likely your hammer. I had this exact problem with a 9mm build a couple years ago. Does your hammer have a cutout at the top of the front face?

 

[Trigger Time]

It doesn't look like your receiver extension tube is screwed in far enough. I bet you can get one more rotation in. Try that first

 

[rvb]

I'm pretty sure the upper/lower won't assemble if their is interference w/ the carrier and buffer retainer. It assembles down over top of the retainer (when you assemble it, the carrier should actually push the buffer back ~1/16" taking tension off the retainer.

if it's binding up on the hammer, check the disonnector functionas a culprit.

It doesn't look like your receiver extension tube is screwed in far enough. I bet you can get one more rotation in. Try that first

he's only got about a half turn before he hits the buffer retainer.

I would also not only swap carriers w/ your RRA, but put your complete RRA upper on and vice verse. It's possible, though less likely, the upper is out of spec causing the carrier to hit the lower or receiver extension. If your new upper works ok on your old lower, you'll help issolate the problem.

-rvb

 

[ForceTA308]

I will do that when I get home tonight. I do know that I am pushing the buffer back the 1/16" and I'm able to assemble the upper to the lower, so that would direct me more towards what you guys are saying with the hammer.

 

[rvb]

1st thing I'd do is take the upper off.
manually cock hammer.
while holding the hammer so it can't crash fwd, pull the trigger and continue to hold the trigger to the rear. The hammer should fall (and you should catch it before it hits the frame).
while still holding the trigger, ease the hammer back down. Does it slip over the disconnector easily, or does it take an exceptional amont of force (it sounds like you have a working rifle to compare it to)?
If it hangs up on the disco, figure out why (disco spring installed wrong, out of spec disco or hammer, broken pin, etc).
If it goes over the disco easily, figure out why the hammer is binding up on the carrier (not able to cock far enough).

Are you comfortable disassembling and re-assembling the lower? you have known good parts in your RRA. Put those fire control parts in your new lower, starting w/ just the hammer, then just the disco, etc to help issolate it. If that works, then you probably just need a new hammer or complete fire control group or FCG part.

-rvb

 

[padawan]

I would try what rvb suggests... I had a friend that installed the disc spring upside down which caused disc/hammer issues. The disc would not compress/swivel in its groove in the trigger. He had a heck of a time getting the bcg back because the hammer would not cock correctly. From your 2nd pic, the buffer retainer pin looks clean (not dinged up from bcg striking it).

 

[rvb]

check the disonnector function.

If it hangs up on the disco, figure out why (disco spring installed wrong ...

I had a friend that installed the disc spring upside down ... He had a heck of a time getting the bcg back

agreed, most likely culprit, which is why I keep focusing there.

-rvb

 

[padawan]

If you are comfortable with r&r the fcg, take it out, take the trigger and disconnector, insert a 'pin' and make sure the disc moves freely in the trigger. If the disc spring is upside down or ?? you'll feel it.

 

[Trigger Time]

You'd figure the guy would notice if the trigger was screwed up but hell I guess not.

 

[rvb]

I just noticed something... your receiver end plate (and maybe castle nut?) seems to be sticking up quite high above the lower receiver. It's not keeping your charging handle from moving, is it? hard to tell from the photo since that's not the in-focus part. there seems to be a "ding" on the endplate at the top... maybe from the CH?

get us a better profile shot of the endplate/castlenut. I'm now thinking you need a new endplate.

-rvb

 

[Denny347]

I just noticed something... your receiver end plate (and maybe castle nut?) seems to be sticking up quite high above the lower receiver. It's not keeping your charging handle from moving, is it? hard to tell from the photo since that's not the in-focus part. there seems to be a "ding" on the endplate at the top... maybe from the CH?

get us a better profile shot of the endplate/castlenut. I'm now thinking you need a new endplate.

-rvb

I didn't notice that until you just said something...that could be an issue.

 

[rvb]

I didn't notice that until you just said something...that could be an issue.

I kept going back to those pictures thinking something didn't look right, but I was focused on the buffer / buffer retainer. Apparently my subconscious knew something I didn't....

-rvb

 

[Trigger Time]

Holy crap good eye!!!