ar upper won't fit??? help

garyz

garyz

NES Member
Joined
Dec 18, 2005
Messages
997
Likes
90
Location
Brockton, ma
Feedback: 48 / 0 / 0
so the fed x guy shows up @ 7ish this morning, according to my wife,
i was already at work. and he has my jse surplus upper.
i have an ati polymer lower. going nuts all day , just wanted to come home
and see my new toy. now the problem.
i attempted to put the upper on the lower, front pin, no problem.
back pin, is a hair out, and the pin won't push through.
i tried squeezing the upper / lower togther, but they are tight.
what are my options? can i file the rear pin hole ? or should i be looking at something
simpler first

thx in advance
garyz
 
I had this issue with a lower once. The rear corners of the upper, the part where the lower pins mate, might be rubbing up against the back inner corners of your lower. I solved this by very very slowly filing away some material in the lower. I confirmed it was my lower because I could not get the rear pin to seat without excessive force in multiple uppers.
 
can't tap it in, when i look from the other side, i see the pin is
hitting the rear hole of the upper, it's up beyone the pin hole.
i don't have another upper to try, the upper appears to be seated
tight w/ the lower, could the rear pin be drilled off center?
 
Something is out of spec from the sound of it. Provided you checked for clearance and the upper isn't hitting anything, than either the hole on the lower or the upper is not correctly located. Can you lean on someone at your local club to gain access to another upper to try and fit? Can you gain access to another lower to try your upper on? Either will help you determine where the fault is.

From there you can decide to fix it yourself - or go back to the manufacturer (which is what I would do)


or.......... you can take a rat tail file and hog out the hole on the upper a bit to allow it to fit the lower. But I would not recommend this. But I've heard of some doing this before...

In my opinion, this is what warranties are for...
 
Last edited:
I would file the lower pin hole before effing the upper. Try it on a normal lower.

Also, try putting the lower in the freezer or oven depending on whether or not it needs to shrink or grow.
-tapatalk and Devin McCourty blow chunks-
 
tried w/ the hammer up and down
the lower is polymer, so not big on filing that
i'll try to see if i can borrow another ar somwhere
and try both upper/lower combos. if that doesn't work,
i'll call the manf. crap was in a really good mood when i found
out the fedex guy came to my house.
 
garyz said:
tried w/ the hammer up and down
the lower is polymer, so not big on filing that
i'll try to see if i can borrow another ar somwhere
and try both upper/lower combos. if that doesn't work,
i'll call the manf. crap was in a really good mood when i found
out the fedex guy came to my house.
Click to expand...

Take a few pics and post them up. I would be looking for flashing in the lower, and maybe taking a few readings with a set of calipers.

The Last polymer lower I built had to be filled a little to get the upper to sit right. That lower now has well over 2k rounds down the pipe with no issues.
 
Could be the upper as well. I had this prob once and I chamfered the rear corners on the back of the rear (upper) pin block. If they fit together well without binding it probably isnt a fit problem. you should find out which hole is out of spec. The lower or the upper. If you have access to another upper and lower it should be apparent when you swap and check the holes. If it is a hole that is just a little out I would have a gunsmith slightly enlarge the hole (oval it) on the upper.

Also do the pins fit easily into the holes when they are separate I.e. are the holes the right size (dia) and are they free of burrs.

fred2386 said:
I had this issue with a lower once. The rear corners of the upper, the part where the lower pins mate, might be rubbing up against the back inner corners of your lower. I solved this by very very slowly filing away some material in the lower. I confirmed it was my lower because I could not get the rear pin to seat without excessive force in multiple uppers.
Click to expand...



Sent from my Galaxy Nexus using Tapatalk 2
 
Last edited:
You said you did front pin first, then back. Try the other way around. Worth a shot (pardon the pun).
 
yeah those polymer lowers seem to a bit wonky spec wise my friend built one and the pins were amazingly tight even after being worked a bit! best of luck!
 
Had a similar problem with a lower. I could see where the upper and lower were not quite a matched fit. I used light sandpaper and kept taking it down a little at a time until it was close enough to bang the pin in with a mallet. I didn't want to go any farther in case the upper was a hair too big. My new upper fits nice and snug so I'm glad I stopped where I did.

If you have access to another upper, try it and see if it hits the same way. If it does, take it down a little or send it back.
 
garyz said:
tried w/ the hammer up and down
the lower is polymer, so not big on filing that
i'll try to see if i can borrow another ar somwhere
and try both upper/lower combos. if that doesn't work,
i'll call the manf. crap was in a really good mood when i found
out the fedex guy came to my house.
Click to expand...

If you need to file the lower receiver hole, keep in mind that it might be better to take just a little off both the front and rear hole to make up the difference, rather than take a lot off just one of the holes.
 
I would find which is out of spec (upper vs lower) and file that... I wouldn't take a part that is in spec and make it out of spec because it basically ruins that part for future use and resale. But like I mentioned in a previous post - I wouldn't file it at all unless it is your only option. This is what warranties are for.

That said, I have read other posts about ATI polymer receivers being out of spec. Lots of info on Google about the bolt catch not being correct in particular. So I would tend to suspect it is your lower that is out of spec upon further reconsideration. Therefor the recommendations of filing the lower would be better than my previous recommendation of filing the upper.

However polymer lowers are weak by design compared to forged receivers. Their cracking and failings are pretty well documented and found via Google. The typical crack/failure involves cracking to that hole as well. So the idea of removing additional material in that spot on the receiver doesn't sit well with me. I really think you should just go back to the manufacturer and get an in spec receiver.
 
Just to elaborate on what I did, I didn't file the hole, I filed where the lower rubbed on the upper. There was a clear contact spot where it was fat and didn't contact smoothly with the upper.

I wouldn't modify the hole where it's already relatively thin. Plus like others have said you could end up with a loose fit against other uppers. Think Banana/Broadway.
 
Depending on how off it is, I would file down the Pin itself. Those are only a couple of bucks and easy to replace if you screw it up. I drill a hole through the retainer that holds the spring/detent in that holds in that pin and tap/cap it off with a 4-40 set screw. If you find that you get another upper and it's too loose with the filed down pin, just remove the set screw and swap out to an unmodified pin.
 
partyboy424 said:
Depending on how off it is, I would file down the Pin itself. Those are only a couple of bucks and easy to replace if you screw it up. I drill a hole through the retainer that holds the spring/detent in that holds in that pin and tap/cap it off with a 4-40 set screw. If you find that you get another upper and it's too loose with the filed down pin, just remove the set screw and swap out to an unmodified pin.
Click to expand...

Couldn't you just use a bolt with some washers?
 
ok went to my local shop, thank you steve at zero hour
he took 1 of the few ar's on the wall split it apart, and put my upper
on their lower, no problem,. their upper would not seat on my lower
so i now know that my lower is out of spec. looks like the flat part of the lower
is out, so i'm going to try to sand down the top of the lower.
steve suggested to run a marker over the top to see where it is high.
i'll keep you informed.
garyz
 
Last edited:
finally got up the nerve to take a file to the lower
15 min or so, multiple file/ and fit tries. finally got it to fit.
really really tight. small problem, the rear pin detent ball went for a ride
so, do i need the rear detent ball/pin.
the rear pin holds the upper, and is super tight, only problem i can see,
is when i take it down to clean it, i'm probably going to lose the rear pin, as i have to punch it out
any thoughts / conerns about the detent that i should think about?
garyz
 
ToddDubya said:
Or a block of wood on one side and a sheetrock screw? Use a fine thread so you can really crank it down.
Click to expand...

Just put an 8 penny nail through, and bend it over with some pliers!

P.S. ;-) and post a picture!
 
Last edited:
garyz said:
finally got up the nerve to take a file to the lower
15 min or so, multiple file/ and fit tries. finally got it to fit.
really really tight. small problem, the rear pin detent ball went for a ride
so, do i need the rear detent ball/pin.
the rear pin holds the upper, and is super tight, only problem i can see,
is when i take it down to clean it, i'm probably going to lose the rear pin, as i have to punch it out
any thoughts / conerns about the detent that i should think about?
garyz
Click to expand...

PM me your address. I'll send you a detent pin. I keep extras
 
ojrvidg_zpscb2a717e.gif


75 DAY OLD THREAD ALERT!

I read the whole thing--you might as well give us an update!
 
bought the polymer lower, just because it was there
at the time. saw it for a good price at the marlboro show
didn't really have any plans, but at the time the price was right
to have it, just in case
 

Similar threads

Help on which Rifle to choose
Replies
18
Views
394
P. Lopes
P. Lopes
Fitting a Shotgun
Replies
12
Views
367
vellnueve
vellnueve
Help with rust prevention on my friend's Browning Citori CXS
Replies
15
Views
445
StephDoza
S
7.5 upper
Replies
4
Views
284
Asaltweapon
Asaltweapon
Help with SA Prodigy plate inquiry
Replies
0
Views
175
jeffC
jeffC
Back
Top Bottom