Rear Take down Pin Won't Go Through Lower and Upper

[hitdank]

Usually mp5 style guns have this problem.

[Seeker]

Try using a Dremel. When I built my rifle the upper and lower did not match up well. I used my Dremel to shave down and remove material from the takedown pin. Now it goes in like butter and comes off just as easily.

[badfish71]

I’m gonna guess position tolerance is no bueno. Most manufacturers overcome this by making the rear takedown hole into an oval.

[Hello_World]

Really appreciate all the responses. I'm going to shoot a few hundred rounds through it to see if it loosens things up a bit.

Unfortunately, this is my first AR, so I don't have any other uppers or lowers and I live in the heart of San Francisco (yes I know, I'm dumb) so hard to fine anyone with an AR aside from range days

I don't think its the trigger assembly. I have a drop in trigger and the receivers still didn't mate with the BCG out.

My next step if shooting doesn't work will just be to take it to a gun smith. Although I'm not sure there are any gun smiths in SF proper.

[God Bless America]

At the range, find somebody with an AR, explain your problem, and offer a box of ammo to see if you can try their upper on your lower for fit.

[bronco75a]

Some ARs are super tight before being shot did you push down on the upper and try tapping it in with a rubber hammer? I would do that then run about 1000 rounds through it. Bet after that it goes in nice and easy.

Run 1000 rounds through it to fix it - you can't be serious.

[Usmc0844spare]

Really appreciate all the responses. I'm going to shoot a few hundred rounds through it to see if it loosens things up a bit.

Unfortunately, this is my first AR, so I don't have any other uppers or lowers and I live in the heart of San Francisco (yes I know, I'm dumb) so hard to fine anyone with an AR aside from range days

I don't think its the trigger assembly. I have a drop in trigger and the receivers still didn't mate with the BCG out.

My next step if shooting doesn't work will just be to take it to a gun smith. Although I'm not sure there are any gun smiths in SF proper.

OK, I realize you have the issue mostly fixed but here is something else to think about. When I assembled mine the pivot pin "ears" on the lower were fairly "robust". When I tried to close it up they would bind on the rail. I think there might be some slight possibility that if this is "barely" happening it could put stuff out of alignment back at the takedown pin.
Mine was enough of a problem that I could not close the thing w/o scraping the crap out of the lower. But I can see a possibility of this happening "just enough" to allow you to close it up but the pins are a tad out of alignment.

Essentially what I mean is, take a look at your rifle and if there is an air gap between the lower pivot pin ears and the rail, you are fine. If they are physically rubbing/touching, this could be causing issues.

I fixed mine by lightly dremeling the part of the rail where it rubbed to give it some relief.

But overall if you got it closed you are probably GTG as it is.

[Skip_Dog]

Shoot it. It will be fine. I had a new rifle that I installed a compmag on. The pin had to be inserted with the help of a rubber mallet. About 500 rounds later the issue is resolved.

[FeuerFrei]

Eugene Stoner's ingenious design is both a blessing and a curse due to it's modularity.

AR clone assembly 101 is fitting the upper & lower together prior to assembly to preview any fitment problems.

Spending a couple of bucks on 2x 1/4" drill bits to check alignment is all it takes to avoid take down/pivot pin problems.

These pins are designed to move with finger pressure only. NOT BFH percussive procedure.

If the pin holes are slightly out of alignment or drill bits won't insert properly, then use the drill bits to align them or clear them. *Reamer bit is best.

*Nothing on this design needs a hammer to assemble except a FSB that needs taper pins removed or installed. *Staking castle nut & gas key bolts.