One of my upper receivers which I have not had mounted on a lower for quite some time due to an issue with the gas block (have to get it removed by ADCO or a local gunsmith) will not fit onto the lower.  The takedown pins do not go into the takedown pin holes.  I did put it in the freezer to see if that would help free up the gas block, but that did not help.  Could this be what has caused the issue with the takedown pin holes?

Another stripped upper goes on the lower just fine, so its not the takedown pins themselves.

The holes are either too small or don't line up, or both.  Figure that out first.

After that, it all depends on "by how much" they're off.

Pics man, post em

Gas block and take down pins are two totally different things.
One has nothing to do with the other.

Now if the takedown pins are tight you have two choices:
1- ream the pinholes in the upper.
2- shoot the thing! The pins will loosen up with use as the upper moves a smidge when fired. This is preferable.

you are putting the front pin in first right?

I know the gas block has nothing to do with the take down pin holes, but I mentioned that because I think putting the upper in the freezer may have affected them.


Yes, I am attempting to put the front take down pin in first, but I can't get the front pin in the hole so the order doesn't really matter.  


Should I try using a dremel to ream out the holes a bit?

Use an actual reamer.

^^^this.
Short of a reamer you could take a 3/16 dowel, cut a slit end wise deep enough for a strip of 400 emery or wetordry paper. Slide it into the pin holes and spin it by hand. Do just enough to let the pin slide in.
Have you checked to make sure there are no burrs on either the pin or holes?


And freezing would have nothing to do with it.

I just fixed an upper/lower pin issue for a guy.

The issue was one a custom upper with an integrated handguard mounting system built into the upper.

The issues were:
Radius cut on upper to clear the front take-down pin "ears" was not large enough
Upper was machined with a corner radius end-mill and lower had sharp edges that interfered with the rounded corners
Tool zero issue during machine left a few high-spot on bottom side of upper that interfered when assembled.

Symptoms: pins had to be beat in/out which caused some minor damage to the lower.

Solution: remachine proper areas of the upper for necessary clearance on lower.

I would look into some/all of the above mentioned issues BEFORE you ream your pin holes. If your pin-holes really are the wrong size then a take-down pin won't fit in them when tried outside of the lower. Have you tried sticking a take-down pin ONLY through the lugs on the upper?

before removing any material you need to figure out what the issue is so you remove the right material

Is the pin hole to small? Is the lug to large causing the hole not to line up?

My advise, take off the front pivot pin and figure out where the interference is. Once you know what the problem is it makes fixing the right issue easy

I'm starting to wonder if perhaps its the handguard pushing against the lower receiver thats preventing the pin from going in.  Either way I think I'm just gonna send the whole thing to ADCO so I don't ruin it any further.

He already stated he couldn't get the front takedown pin in, but I'm not quite sure how a front hanguard would interfere with getting a pivot pin in so ...

See if this works. OP you want your AR to look like this with the pivot pin in, there really is no way the front handguard can interfere with this.

image

I have taken some pictures so you folks can see what is actually going on here.

I've already tried that.  When I have it "open" and try to put just the front pin in it makes a clicking sound and feels as though the pin is bottoming against a ridge, but I can't see anything sticking out.  What I think is happening is that the handguard locking ring is pressing against the lower receiver preventing the pin from lining up with the hole properly.

clean the paint off the outside and inside of the lugs...

if you don't have acetone use fingernail polish with acetone....

It has been determined that the issue is the handguard barrel nut locking ring, not paint.  Its been a while since I put the handguard on.. so I'm going to have to find a place to mount my vice.  Am I supposed to turn the handguard counter clockwise WHILE holding the locking ring still with the wrench to loosen the handguard, and then back the locking ring off towards the muzzle end once there's some room for it to move?  Or is it threaded the other way?

If it has a gas tube goint through it, you would have to take the gass block and gas tube off first. BUT loosening that would not work as I believe it is also the barrel nut. I could be wrong, I haven't dealt with that handguard.

It looks very close to fitting. If it was me, I would lightly tap the pivot pin with a soft mallet to try and force it home. (I'm not talking hitting it with a hammer here but  a little more force might bring it home)

If it works, oil the hell out of it and pivot it around a bunch to see if it gets better. then same for the takedown pin but instead of pivoting it, go shoot a mag through it

Then take it apart, inspect and clean. See if there are any shiny spots from rubbing.

It remains a lot more work to put metal back than remove it.
Caution is justified.

Drills ALWAYS make larger than nominal holes.
By at least a few thou.

Reamers are for precision diameters.

make SURE you need to remove metal.
Drill undersize.
Ream to final size (or even a thou under).

edit: woops wrong thread

Loosen the locking nut, back the handguard off a couple of turns and re tighten the locking nut.
Problem solved.

Yup this...

Yup, first thing I noticed with the pictures; handguard is screw on way too far...

Normal right-hand thread so you would want to turn the handguard CCW as you're looking from the muzzle end.


The YHM lightweight handguards have an independent barrel nut. The parts he needs to move will not have any bearing on the  barrel nut so no gas-tube work is necessary.

Also, I would highly suggest people not follow your advice. It's pretty clear from the pictures that the hand-guard and lock-ring are installed too far onto the upper receiver and it's causing quite a binding issue. Tapping the pin home and pivoting the upper/lower will do nothing except chew up the lower receiver lugs and possibly damage the threads on the lock-ring (preventing future hand-guard disassembly). This is a case where the fix is so simple to do right there is NO reason to even suggest a half-assed shortcut to solving the problem.

No Shit, I gathered that from the other who were familiar with that forearm. I highlighted my comments for emphasis and they were given with respect to a fixed barrel nut that would not have that option. But thanks for joining the conversation a week late!

What's your point?

That beneficial suggestions can't be made unless done-so within 1 week of the last reply to the thread?

Or are you somehow trying to make yourself feel better about your half-assed suggestions by being demeaning to me? The instances where driving the take-down pins in with a hammer and using a little lubricant to cover-up the symptoms of ill-fitting parts is almost NEVER a good idea. Why would you even suggest it?

I get that you were trying to be helpful, my comments were merely to make it clear that #1 your understanding of the YHM forearm system was not accurate that therefore your comments weren't applicable (yes, that part was covered in lesser detail by a couple others prior to my post) and that #2 your advice of brute-force, half-assed attempt to fix it was poor advice (that part wasn't covered by others prior to my post).

That being said, I see this crap all the time. Somebody that doesn't have a good aptitude at mechanics & functions/fitment thereof often do more damage than good by trying to fix things your way. Then I get paid to fix their screw-ups... honestly I'd rather not mess with fixing people's screw-ups, I don't enjoy it and it's not why I work on guns...


Oh crap, I just realized I'm a week late again... guess my comments are all invalid because I missed the week limit...