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9/19/2017 7:27:10 PM
Posted: 2/23/2006 1:24:41 PM EDT
I took delivery of my second AR about a month ago. It's a Colt LE6920, my other is a Colt LE6520. My question relates to the amount of play that is allowable between an upper and a lower. I guess you call it roll. That is, when in shooting position with one hand on the pistol grip and one on the handguard if you roll your wrists ( I know, I know, no one who hangs around here has any limp writsts how
I was wondering if there is a spec you could check with a feeler guage or something of that nature. Barring that, is there any way to tighten them up or do I need to have smith look at it.

I can run a guage in there tonight and let you know how big the gap is.

Thanks for any info or opinions.

Link Posted: 2/23/2006 1:28:06 PM EDT
some play is ok, where in Texas are you? I'm in Houston, if your near I'll take a look at it, but if it's a problem for you get the wedge
Link Posted: 2/23/2006 1:35:53 PM EDT
[Last Edit: 2/23/2006 1:37:55 PM EDT by Stickman]
Link Posted: 2/23/2006 1:38:43 PM EDT
I too am in Houston. I would love to have another to compare it with. I'm on the west side in Katy, but drive around town for work virutally every day. Let me know what would be convenient.
Link Posted: 2/23/2006 1:55:46 PM EDT
[Last Edit: 2/23/2006 1:59:53 PM EDT by want2race]
Yes there is a standard, it's in the 23&P manual. I'll look tomorrow but I believe it is a .020 feeler gage. If the gage passes between the upper and lower it fails. It's the only gage inspection that can kill a lower receiver (from being servicable).

I also use the common sense approach, if the gage fits the gap for "a good portion of the receiver", then I consider it a fail. Not just one spot.

But yes, this is according to the Army TM.
Link Posted: 2/23/2006 4:08:04 PM EDT
This is my first post to this forum, and I just bought my first AR a LE6920 and live out in Katy too. If you would like another 6920 to compare it to you can IM me. I found a little bit of play in mine but it wasn't enough to make me concerned. This is a great forum and has answered a lot of my questions without even having to ask.
Link Posted: 2/23/2006 4:30:40 PM EDT
The only time I've had no play, or at least VERY little is with the SR-25's/MK11's. Knights has front and rear pins in .005" increments and I can tune the upper to fit the lower with very little play.

Does it matter that much? Depends on your intended use.
Link Posted: 2/23/2006 5:15:29 PM EDT

Originally Posted By want2race:
Yes there is a standard, it's in the 23&P manual. I'll look tomorrow but I believe it is a .020 feeler gage. If the gage passes between the upper and lower it fails. It's the only gage inspection that can kill a lower receiver (from being servicable).

I also use the common sense approach, if the gage fits the gap for "a good portion of the receiver", then I consider it a fail. Not just one spot.

But yes, this is according to the Army TM.



I always wondered about this, some of my Colt M-one-6's(<--sorry lost a digit) had incredible slop between receivers. A few of them could have easily gone past the .020 spec, but they were still incredibly accurate. The play was a concern of mine when it came to accuracy, however the first shot downrange proved otherwise. The Colt A2's were the first rifles that were tight, but of course they were brand new when we got them.
Link Posted: 2/23/2006 7:04:13 PM EDT
Well I pulled out th feeler guage when I got home and it appears that I have a range of between .010 and .012 at all points between the upper and lower. That seems safely within the previously posted limit of .020.

Want2race, if you get a chance to look up and verify that spec tomorrow as you said, I would appreciate it.

Thanks for all you guys help.
Link Posted: 2/23/2006 7:31:16 PM EDT
0.087" of play?
Link Posted: 2/23/2006 7:49:39 PM EDT
is this the gauge test you are talking about?


1. With the upper receiver attached to the lower receiver, and the pivot pin and takedown pins in place, perform the
following test:

(a) Apply hand pressure to push the upper receiver as far to one side as possible.

(b) Attempt to insert a 0.020 inch thickness gage between the pivot pin lugs of the upper and lower
receivers.

(c) If the thickness gage penetrates to the pivot pin at all accessible locations, repair by replacement of the upper receiver (see (b) below) or replacement of rifle is required.

2. If the rifle fails the above test, remove the upper receiver and install a "NEW" upper receiver and perform the test again.

3. If the rifle now passes the above test, it shall be considered serviceable and continue in use.

4. If the rifle falls the test with a new upper receiver, this failure shall be considered a shortcoming. This shortcoming requires action to obtain a replacement rifle. Once a replacement has been received, evacuate the original rifle to depot for overhaul.

Link Posted: 2/23/2006 8:49:57 PM EDT
[Last Edit: 2/23/2006 8:55:01 PM EDT by ru4freedom]
Just a touch of barrel bedding compound, Acura-Glass, Micro-Bed, ect.... will make em' fit good & tight. I always bond the bedding compound to the upper & use the release compound on the lower just in case I want to use that lower with other uppers!!

If you use that upper on differant lowers this might not be the way to go for you!!

The official formula is as follows:

AR + Bedding Compound = ZERO Play!!



Link Posted: 2/23/2006 9:09:17 PM EDT

Originally Posted By Gunzilla:
is this the gauge test you are talking about?


1. With the upper receiver attached to the lower receiver, and the pivot pin and takedown pins in place, perform the
following test:

(a) Apply hand pressure to push the upper receiver as far to one side as possible.

(b) Attempt to insert a 0.020 inch thickness gage between the pivot pin lugs of the upper and lower
receivers.

(c) If the thickness gage penetrates to the pivot pin at all accessible locations, repair by replacement of the upper receiver (see (b) below) or replacement of rifle is required.

2. If the rifle fails the above test, remove the upper receiver and install a "NEW" upper receiver and perform the test again.

3. If the rifle now passes the above test, it shall be considered serviceable and continue in use.

4. If the rifle falls the test with a new upper receiver, this failure shall be considered a shortcoming. This shortcoming requires action to obtain a replacement rifle. Once a replacement has been received, evacuate the original rifle to depot for overhaul.




I found that test after Want2Race mentioned the 23&P manual. What I was originally referring to was the max and min distance between the edges of the upper and lower on each side. Look at the photo posted by Stickman above. Thats the gap I was measuring.

I found the 23&P test after that, but I don't have a feeler guage on hand the will penetrate to the pivot pin. I guess thats a good thing.he
Link Posted: 2/24/2006 3:32:39 AM EDT
The max width between the lower receiver lobes (front pivot pin area) is 0.515".

If it fails the .020, you can check the lower to make sure it's within spec.
Link Posted: 2/24/2006 3:50:44 AM EDT
way too much "play" or "space" would allow the carrier to strike the lower reciever at the buffer tube area.


but im sure it would have really wide cause i have an e.a. lower with colt upper that has a mean gap between the recievers with no problems.
Link Posted: 2/24/2006 6:56:23 AM EDT
Thanks for that infor Want2race I'll have the calipers out tonight. Well, maybe not. maybe I'll just go shoot the damn thing
Link Posted: 2/24/2006 8:17:40 AM EDT

Originally Posted By ru4freedom:
Just a touch of barrel bedding compound, Acura-Glass, Micro-Bed, ect.... will make em' fit good & tight. I always bond the bedding compound to the upper & use the release compound on the lower just in case I want to use that lower with other uppers!!

If you use that upper on differant lowers this might not be the way to go for you!!

The official formula is as follows:

AR + Bedding Compound = ZERO Play!!






I wondered if that would work. Could you please go into detail.
Link Posted: 2/24/2006 3:26:52 PM EDT
[Last Edit: 2/24/2006 3:38:50 PM EDT by 200-10x]
The Army marksmanship team used to use epoxy to "true" up the fit between uppers and lowers... and stopped doing it as they found it made little or no difference in the accuracy of the rifle. Also, as mentioned above, it can preclude your ability to switch uppers from weapon to weapon.

Simplest technique: Open lower. Run a strip of scotch tape along the edge of the upper on the outside edge to form a "dam". Coat lower with release agent. Run a thin bead of epoxy along the edge of the upper against the dam. Gently close and secure with the takedown pin. Let set. File the excess off along the inside edge...... then enjoy your tight fit, but don't complain about how it leaked out along the tape and spoiled the perfect look.... THEN, remember that after all that, the Marksmanship team gave it all up because they found it didn't effect anything of significance.

If the rattle bothers you, use an accuwedge to stop the rattle (I can understand though if you're into spec's and feeler guages and what's standard it WOULD bother you (not a dig I work with alot of machinists that would stroke out shooting some of the rattle traps I've seen)).

Some people do so far as to use a rear take-down pin that can take up the slack. check them out here: jprifles click on "rifle parts" and look for "tension pin".
They work, but makes takedown a b*tch though.

I know it seems counter-intuitive, but it really doesn't matter.... it won't effect accuracy, it just bothers people.

ETA: you can't BELIEVE how hard it is to resist comment about Colt QC...... shoot, I said it anyway, sorry......
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