Upper & Lower fit: too tight?

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Hello, this is my first AR build. I know usually the fitment is looser than desired and one would use an accu-wedge. I've found just the opposite. I have an Anderson multi-cal lower mated to an Anderson 16" stainless 5.56 upper that came as an assembly with bcg. I'm using an unbranded lpk. The pins are not oversized. All parts were purchased at different times from different vendors. No fitment issues with handguard. The first two times I tried to fit it and it wouldn't go so I disassembled the lower and started over, oiling and checking fitment as I went. The third and final time is when I decided its just going to be a very tight fit. I had to turn it upside down on the floor and bear down as hard as I could to get the takedown pin inserted and I'm 6'2" 210lbs. Everything functions perfectly and I couldn't be happier with it. Now to disassemble and clean it, I need to use some type of vise or clamp to relieve the pressure to remove the pin, definitely not able to easily disassemble in the field as designed. I'm sure it will loosen some with use but should I be concerned with this or happy that I got a very tight fitting rifle? Thank you
 

drgrant

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That's kind of f***ed, I would say that one half or another is out of spec, would be hard to tell unless you had other uppers or lowers to swap with, though.

-Mike
 
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Are you saying you have to press the upper and lower together to get the holes to line up? The rear holes or the front holes? Did you try a different pin?
 

ReluctantDecoy

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Just out of curiosity, did you try installing the pins in opposite order? I assume most do pivot first, then rear take down. If you do the takedown first and it goes in without issue, then I'd assume either the spacing between the two pivot pin holes is somehow out of spec or even a slight warp to mating surfaces during heat treat. This is particularly true if the pivot pin previously went in like normal, but has issues as the second pin. If you still have issues with just the rear takedown first, then maybe the actual drilled hole for the rear takedown is out of alignment. Just my 2 cents though.
 

dlarge

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I had this issue with a matched Anderson. Really annoying. It was the upper. I tossed it. Lesson learned.
 

jayhitek

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oil both pins and the mating holes.
If you get the rear pin open..
While holding the upper and lower closed, Does the front pin move in and out easily?
And vise versa, if you can get the front pin open, holding the upper and lower together, can you now open and close the rear pin easily?

As a test.. Try another upper and see if it's the same problem. In MA The holes on the upper are easier to adjust and safer than messing with the lower.
Before you tweak the upper try to determine if you made the rear hole on the upper a hair larger would resolve your problem.

I had to do this with a cheap used CZ 22 upper.. I drilled out the rear hole of the upper to make it possible to take down without using a punch and pliers.
 

Cap'n Mike

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At one point I had 2 complete uppers and 2 complete lowers, all 4 purchased separately from LMT.
One upper and one lower combo was so tight I couldnt get them together.
Luckily I was able to mix and match between the four parts so both guns worked fine.
I chocked it up to the chances you take not buying complete guns, as quality control would probably catch that at the factory.

If you figure out which hole in the upper is out of spec, you could try wrapping a piece of sandpaper around a dowel and enlarging the hole in the correct direction (probably down toward the lower) til it fits.
It probably wont take much, just polishing it with fine grit will probably work.
 
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I havent tried swapping anything yet. Its as if you were to put in a rubber wedge that's too large and the upper just doesn't want to go down the last 3/16" without alot of force. The holes line up perfectly, before I assembled the lower I fit it to the upper to check, that's why I kept taking apart the lower and re-doing it thinking something in the lpk was off. I will take all of your suggestions and check it out in the next day or so. I greatly appreciate the help. @Tackdriver I'm not too close to you but I bought some mags from you in the past. If I cant figure it out I will take you up on the offer, and will give me a reason to go pick up some more mags if there are any left. Thanks again everyone, Brennan
 

SJan

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All of my builds have been pretty damn tight when new. A little oil on the OD of the pins, as well as in the channel where the detent rides, work the pins in and out of the lower a bit. After you shoot 100 rounds or so the pins will move easier.
 

84ta406

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If you're in the Worcester area I have a couple uppers and lowers that we can try out and see what fits and what doesnt. Just curious but do they fit any different with the BCG removed?
 

CrackPot

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Sometimes things are on the hairy edge of spec (or just over). Variable thickness in anodization can push it over. Never force it. If you are anywhere near Littleton I am happy to help. I’ve sometimes needed to slightly extend the takedown hole in the upper or take some material off the back of an upper to get a good fit. I have a milling machine so the hole extension is easy. Cold blue and all is good.
 

snax

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Most guys would be happy with a nice, tight, virgin gun.
Tight, like a shop vise hammered shut with a mallet.
You like loose, get a nice, gently used AK. I hear they run a bit sloppy and wet.

Do anderson uppers have issues with fitting regular lowers? Primary Arms had a sale on the uppers for 35 dollars each. So i bought two. They should be arriving in a few weeks.
I may have experience with some new andersens. More than two, but less than ten.... All fit excellent, no issues, and uppers swapped around with lowers no problems. This is both with open lowers and closed lowers.
Also test fitted SW MP upper, Ruger upper, and BCM upper with some of the lowers, no problems.
My guess is one or both out of spec. Test upper with different lowers, lower with different uppers.
 

one-eyed Jack

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A lifetime ago I had a tour of the shop in Maine where they were putting M16s together. You know the company. On the ass'y line they were mating lowers to uppers. The gal would put in one pin and run a bit on a pistol drill thru the other hole without trying it first. The pin went in, no problem. Then a guy at the end of the line ran off a 30 rd mag full auto into a hole in a concrete wall and put the gun in a box. Jack.
 

Stryker

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Sometimes things are on the hairy edge of spec (or just over). Variable thickness in anodization can push it over. Never force it. If you are anywhere near Littleton I am happy to help. I’ve sometimes needed to slightly extend the takedown hole in the upper or take some material off the back of an upper to get a good fit. I have a milling machine so the hole extension is easy. Cold blue and all is good.

+1

Across all of my builds I have only had one where I couldn't close the takedown pin - all it took was a couple passes with a round file inside the takedown hole to make it work. It took off very little material (probably indeed just anodization) but made for a tight but operable fit.
 

CrackPot

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Do anderson uppers have issues with fitting regular lowers? Primary Arms had a sale on the uppers for 35 dollars each. So i bought two. They should be arriving in a few weeks.
I've built 10s of ARs all using Anderson uppers. I have never had an Anderson upper problem. When I have isolated the spec non-conformance it has always turned out to be the lower. I stopped using Noreen Billet lowers as a result. But nothing has ever been so bad that a file or a quick hole extension on the mill did not fix the issue.

The specs and tolerances are such that everything can be in spec and you can still have a REAL tight fight. Building ARs is not just putting random parts together. Some fitting can and will be required on some builds. It is just part of the process.

As I said to the OP, bring it to Littleton and I will get it together tweaking whatever needs to be tweaked
 

ArpNet

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This is one of those vague posts that may or may not help. I bought a new BCG and upper for my Colt lower with a sear block. When I went to close it, the upper wouldn't close all of the way. The BCG was hitting the sear block. Found out that is why the original BCG was an odd shape on the Colt. Had the sear blocker removed for that reason and to put in drop in triggers. Doesn't sound like your issue but exhibited the exact same symptoms so I thought I would mention it.
 
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Solved! Removed BCG and buffer, no difference. Removed receiver tube and fit perfect. Lack of attention to detail and assembly in ill-illuminated room revealed cheap receiver tube had small piece of threaded metal not sanded down after threading and cutting it so the surface wasn’t flat. I’ll take it to work tomorrow and smooth out and refit it. Thank you to everyone for your input and offers to help.
 
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Yes receiver tube / buffer tube. Just a cheap tube so I didn’t expect much. If upper receiver was hitting it, other than the piece of metal sticking out, is it possible I had it in one turn too much as well? It wasn’t touching the nipple on the plunger so I thought it was good. Either way I’ll know tomorrow when I fix it and reassemble.
 
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