Which AR 15 type rifle?

Old Faithful. Works great for my Sig229 and my Shield.

 

I'm pretty happy with the Adams Arms blem carbine!

 

Here she is.

 

Nice glass.

 

Wifey got me a pretty sweet birthday present. I should be able to pick up the lower tomorrow. It's a Mega-Arms mlok 16" handguard/upper receiver set. I'm gonna build either an SPR or maybe just go all out precision with a target crowned barrel.

 

Been picking away slowly (like whenever there is a sale) on my 10.5" 300blk pistol build. Lower had been done for a while now, recently picked up a stripped upper, and the rear takedown pin will not engage. First time this has happened to me, I've built 7 ARs. Funny thing is the upper and lower are both from the same manu.

So what's the recommended process? Gently take some away from the takedown pin holes, or off of the back of the upper? (that's where it looks like the interference is.

 

If I place the upper onto the lower and do not engage the forward pin, neither of the pins will engage. I can only get the forward pin in when it is tilted up, and that makes me believe the rear of the upper is a little long. looks like that too when viewing through the holes. Should I lightly sand the rear of the upper, or just eat it and buy another one?

 

What brand?

 

Anderson Manufacturing

 

Does that problem upper fit on any other lowers you have so that the pins slide through as they're supposed to? If you have narrowed it down to the upper being the problem, call Anderson up and see what they'll do for you. Worst case scenario, you have to file the rear lug of the upper to make it fit. I wouldn't try filing the lower though. The rear portion of the lower is where all of the stress is when firing. Besides that, the lower would show any sloppiness, while the upper would be hidden. Hopefully we're talking a few thousandths of an inch here.

Not only that, but if you mess with the lower and it still doesn't work out, you'll have to get another and do another 4473 for it.

EDIT: is the pin hitting resistance vertically or horizontally?

 

Yep, everything you just said is why I would never consider touching the lower. Ima go try this upper in my other guns and see what's up.

 

Well, this blows. That upper fits on all my other ARs like a damn glove. Guess I am gonna be messing with the lower.

 

do any of the other uppers fit on the lower? Check that first.....sometimes the +/- tolerance stack doesn't add up on multiple 'in-spec' parts.

 

It might, I didn't check. It really doesn't matter, it's registered as a pistol lower so I can't just swap it to another gun. I'll just go slow and clean up the rear of the lower.

 

Well that sucks! Another thing to try would be to just take the pistol set and put the front pin in, then open and close it a bunch and see if it gets better on its own. Apparently a bunch of the Stags were a tight fit and that was Stag's recommended remedy. Be sure that if you have to take away any of the rear potion of the lower that you don't accidentally mill away too much and add another hole above the selector.

 

It's gonna take more than that, unfortunetely. It's seriously off, like in the hundreths, not thous. It sucks, but I've had pretty good luck previously piecing ARs together with zero issues, I was due. No biggie, I'll make it work.

I hope.

 

Send it back, and get a good one. if they screwed that hole up, what about the others?

I have a feeling that when people start getting around to putting together all those panic buy stripped lowers, Anderson and their ilk are going to magically disappear when the rejects start coming back. Get ahead of the curve.

 

Never, file the LOWER take down pin holes - ALWAYS file the upper (rear) to fit ...

 

It's not just one hole, both are off by the same amount. The rear of the lower itself, just behind the 'shelf' is too big.

FYI I bought this lower over a year ago, IIRC that was not a panic time.

Not gonna file the the holes, that's hack shit. See above.

 

I know. It was a joke about making it auto sear capable.