if you build enough ARs, you'll run into this. The upper and lower fit together, but it's a little sloppy. You were really hoping for a nice, tight fit and you're disappointed, right? I know I was. It doesn't matter what brand--every manufacturer runs into this problem eventually due to tooling wear. You can send the upper and lower back and hope the replacements are better matched. Unfortunately, you don't know which part is on the outside limits of acceptable tolerances, so you have to send both....which results in more shipping/handling fees, FFL transfer fees, etc. Thanks, but no thanks--not when it's this easy and doesn't permanently modify anything.




first things first: There's the Accuwedge. It's just a piece of red rubber that fits behind the rear pin, and wedges everything nice and tight...sometimes. **note: why pay $6 + shipping for a piece of rubber when a common pencil eraser and a few seconds with a sharp knife accomplishes the same thing?




Unfortunately, this doesn't always work. If it doesn't improve your fit, it's because your loose tolerances aren't at the back lug--it's at the front lug.

If you have a loose fitting upper/lower, give this a try. Separate the upper from the lower. Put a rubber band around the front lug and pin the receivers back together. Big difference, eh?

The problem with the rubber bands is that they break down over time and exposure to UV light and oils. It's a temporary fix at best. here's what works for me:

JB Weld

separate upper/lower, and put a dab of JB around the front lug. While it's setting, lube the lower with graphite, Rem Dry Lube, or a very thin coating of grease. When the JB is dry enough that it doesn't readily take a fingerprint, reassemble the upper/lower. (flex it at the hinge point once or twice to ensure you have clearance)

separate the receivers again and let the JB fully cure. Viola. Nice and tight.







the beautiful thing about these quick fixes is that nothing is permanent. If you move the upper to another lower, and it's too tight, or you want to sell the parts, just use a razor blade to remove the JB. You've only added about .005", and it'll shave right off. The Accuwedge/eraser simply falls out when you break it open.




also of note, is that you can't see anything when the rifle is assembled....no ugly patch job

Dude.. You and that JB weld are dangerous...

I think I need to start calling you JB.

You can do a lot with that stuff.
It's like Duct tapes big brother.

duct tape and JB Weld are like the Force. They each have a light side and a dark side, and they hold the Universe together.

Good job Colt and most of the guys are very familiar with the Accuwedge especially if they own a Colt AR15.

cool little trick there. i've never run into the problem personally, but that is probably because i'm so new at this. but i WILL keep it in mind for future reference.

Great tip Colt45Guy!... and another hats off to JB Weld.

stay tuned for our next episode:



"Repairing Cherynoble. Duct tape, JB Weld and introducing.....BAILING WIRE!"

And he has all these readily available....

Will any of that work for a side to side problem? My son's has a tiny bit of movement keft to right but seems tight if you try to move it up and down. The gun is accurate and runs great, so I don't want to go overboard with it. thx

I have JB weld around because it has saved my butt numerous times in the automotive dept. Thanx for the great idea, going to give this a try tonite !!

This post has been edited by 1000ydstare: November 6th 2008 12:25 PM

Don't forget the hot glue!