AR15 front pivot pin binding

[TGS]

All,

So today I assembled the lower for my new BCM upper that arrived. After punching the front pivot pin on final assembly with the upper, it began to bind and is pretty much jammed in there.

I can still open the gun via the rear pin, but it requires me to force it open with a minor amount of work as opposed to it swinging freely.

This doesn't really effect anything in reality as of right now, but I'm wondering if you guys could diagnose what went wrong when it got put together. It takes a punch and some hard whacks to move the pivot pin from the assembled position.

[spelingmastir]

Sounds like it could be a tolerance stack issue. What brand lower and pins are you using? I assemble lowers using Battle Arms pins as they are made slightly smaller in diameter and are extra easy to install.

[TGS]

Sounds like it could be a tolerance stack issue. What brand lower and pins are you using? I assemble lowers using Battle Arms pins as they are made slightly smaller in diameter and are extra easy to install.

It worked fine when I installed them on the lower. It was only when I put the lower and upper together that it had problems. I dont think it's the upper, because I put the upper on other lowers without issue.

So, something must've bent/broken. Is it possible for the detent or detent spring to become dislodged or damaged in some way that would impinge free movement of the pin?

[spelingmastir]

It could still be an issue with a large pin + lower dimensions + upper dimensions causing it to be extra tight. If the pin can go in and out without the upper on, I'm guessing this is the case. The Battle Arms pins were designed for this type of situation.

[ASH556]

Without seeing it firsthand, I also agree with tolerance stack. I've seen multiple uppers and lowers that were just on the edge of spec and would fit fine with one and super tight with another. I have seen fewer problems with Colt parts. We had to send back a whole shipment of RRA lowers due to this.

[Wayne Dobbs]

All,

So today I assembled the lower for my new BCM upper that arrived. After punching the front pivot pin on final assembly with the upper, it began to bind and is pretty much jammed in there.

I can still open the gun via the rear pin, but it requires me to force it open with a minor amount of work as opposed to it swinging freely.

This doesn't really effect anything in reality as of right now, but I'm wondering if you guys could diagnose what went wrong when it got put together. It takes a punch and some hard whacks to move the pivot pin from the assembled position.

As stated several times, you almost certainly have an out of spec lower. What brand is it?

[M2CattleCo]

I had that issue one time and the front pin was bent. Was a BCM lower and upper. No clue how it got bent, but I put a new pin in and it's fine.

[TAZ]

Have a similar issue with an Aero Precision Lower. My WOA upper that fits EVERY other lower I have (STAG and MEGA) will just not fit the Aero. The last pin to be pushed in needs a hammer. My BCM uppers fit the Aero lower fine. Its a goofy tolerance stack that nothing fixes (tried the BA pins to no avail). Gave up and dedicated that unit as my son's rifle. Has many rounds through it without an issue.