AR upper and lower fitment

[Pwilliams1]

I recently finished an ar build, everything works as intended, but the upper and lower are extremely tight. Tight enough that I have to use a hammer and punch to get them apart. None of my other rifles have been this difficult to disassemble. All rifles are built on stag uppers and lowers. I'm wondering if this could cause any wear issues long term.

I'm probably a little over concerned because this is a pre ban lower, I want to make sure I don't damage it unnecessarily.

Other uppers fit fine on this lower, so I think the issue is coming from the upper side. Should I leave it alone, or have someone look at it?

 

[jimbobborg]

Check that the locking pins aren't bent now. Learned that one the hard way.

 

[dontpanic]

You should mark these as a matched pair. People spend money to get a tight fit like that. Use this set when you decide to build a super accurate gun.

 

[Boom Boom]

Leave it alone. Most people wish the fit was that good.

 

[outrider58]

You should mark these as a matched pair. People spend money to get a tight fit like that. Use this set when you decide to build a super accurate gun.

Second

 

[lx1x]

Snug is fine.. Tight.. Not so. Specially if you using hammer to take it apart.

 

[Pwilliams1]

I know you ideally want a good fit, but this seems like too much. It's tough to explain without actually handling it. It feels like maybe the pin holes in the upper are too tight, or maybe not perfectly straight

 

[amoebicmagician]

don't change anything!!!

The fitment will become looser as time goes on, and people go through long lengths to get their receivers mated together tightly.

Big deal, you use a brass punch for the first couple of cleanings to get the pins out.

Are you sure your rear retainer detent and spring are situated correctly?

Anyways, the tighter that fit, the more accurate your rifle will be.

Eventually it will loosen up, until then enjoy the ride, you will not see any undue wear because of a tight upper/lower fit

 

[amoebicmagician]

if the upper holes are really too small, you can use a dremel with some buffing compound on a felt buffing attachment and polish the inside of the holes.

I would be leary of doing anything more aggressive than that because if you go through the anodizing, you really will have some undue wear from the softer aluminum being exposed.

I would just let it wear in

 

[Pwilliams1]

Thanks everyone

 

[cobra]

If you suspect the holes in the upper are too small. How do the pins fit when pushing them into the upper only while seperated from the lower?

 

[Pwilliams1]

If you suspect the holes in the upper are too small. How do the pins fit when pushing them into the upper only while seperated from the lower?

Haven't tried that. I'll give it a shot when i have a few minutes to take them out of the lower.

 

[outrider58]

...and it might be that the pin lugs may be a little out of spec length wise. Either too close together or too far apart. Does the upper have any play from side to side or front to back at all?

 

[Pwilliams1]

...and it might be that the pin lugs may be a little out of spec length wise. Either too close together or too far apart. Does the upper have any play from side to side or front to back at all?

Nope. Locks up rock solid, like I have to force the upper closed enough to get the pins in, and even then need a hammer to get them in

 

[l730dc]

Sometimes new builds are just tight at first and just need working (i dont know how tight you are talking about though)

 

[outrider58]

Then I would go back to what BoomBoom said. Maybe it will get a little easier once the gun gets shot in but, like many things in life, tighter is better than looser.

 

[Pwilliams1]

Lol. I'll dump a bunch of rounds through it when it warms up and take it from there. My main concern is damage, but it sounds like it's not much to worry about

 

[BradMacc82]

Not an issue, have a few set-ups that are really snug like that.

 

[Pwilliams1]

So after messing with it tonight, I think the lug in the upper does not exactly line up with the holes in the lower. Pin goes straight through without the upper, and goes through with the upper on, to the point that it contacts the lower on the other side. It's either loosened up a little already, or I've had too many bourbons tonight, because it seems easier to remove/insert than before. I'll give it some time and see how it goes. Thanks everyone for the input.

 

[l730dc]

Yeah its just new.. work the pins threw and push them out a bunch of times and itll get better