How much slop is tolerable in the Upper/Lower receiver fit on an AR?

[Lone_Gunman]

I was looking at three different Bushmaster ARs. On one, the upper/lower receiver fit was very nice, with very little movement when i tried to wobble the two. On the second, there was a little bit more, but still not too bad. On the third, I can move the upper and lower recievers enough to see about 1mm of a crack between the two. This wobbles enough to be noticeable when shouldering the rifle.

How much slop is acceptable?
Does this degrade accuracy?
Can anything be done to improve upper/lower receiver fit in an AR?

 

[ants]

It can be as tight as you want it, or as loose as you feel. It makes no difference on accuracy nor reliability. The barrel, sights and bolt are all in the upper.

You can ream the takedown and pivot pin holes and insert oversize pins. If you wanna go that far.

They make rubber shock buffers for $5 that go in the lower beneath the takedown pin. You trim it to the right size so it gets pinched snug between the upper and lower, then insert the pin. The gap is still between upper and lower, but it doesn't rattle. Some owners claim to use a rubber o-ring, but I've never been happy with that.

I build my own AR-15 rifles and compete in IPSC 3-gun. All my rifles are loose between upper and lower. The rattle is meaningless to me, and I manage to win my share of rifle stages in Tactical Class regularly. So it's up to you, Lone-Gunman. To rattle, or not to rattle. Your choice.

 

[Lone_Gunman]

If there is a quick and easy way to tighten up the fit so there is no detectable movement between the upper and lower when I shoulder the rifle, I would be interested.

I dont really care if there is any gap between the receivers as long as it doesnt move. The movement just feels bad to me.

Who makes the rubber buffer you are talking about?

 

[tnieto2004]

http://www.cheaperthandirt.com/ARR006-3292-2701.html

 

[Lone_Gunman]

any other advice?

 

[Babalouie]

Lone_Gunman

How much slop is acceptable?
Does this degrade accuracy?
Can anything be done to improve upper/lower receiver fit in an AR?
__________________

I hated (past tense) the slop too. No it does not degrade accuracy. Yes, this is what can be done: Replace the connector pin with a JP tension pin. Its not cheap ($35) but it tightens it up rock solid. Best money I spent on my AR. Here's a pic and the link:

http://www.jprifles.com/1.5.1.7.php

 

[rcmodel]

Just go with the little rubber Accu-Wedge.
It takes all the rattle out, and you can still get the pins out without tools & a hammer.


rcmodel

 

[MudPuppy]

Do a search on the accu-wedge before deciding upon that. Someone here mentioned one of those coming loose and getting wedged in the FCG, resulting in a major malfunction. If it's a target gun or carbine match shooter, no big loss, but if your life is relying on its function, be careful with decisions like this.

 

[Walkalong]

I had an Accu Wedge in my Bushmaster, which had a bit of play, and it worked great. It was still in it when I gave it to my nephew when he got out of the Marines.

 

[Chipperman]

Someone here mentioned one of those coming loose and getting wedged in the FCG

I can't see that happening while the gun is assembled. It must have fallen into the lower while the gun was open and the operator did not notice.

 

[aloharover]

If there is a quick and easy way to tighten up the fit so there is no detectable movement between the upper and lower when I shoulder the rifle, I would be interested.

Yeah, get a paper match book cover from you MRE accessory pack.
Shotgun the action.
Insert the cardboard cover between the upper and lower just in front of the buffer tube.

You can also tear the cover into small squares and place them inside the lower, under where the rear upper lug fits. Basically shimming it like the accuwedge does.

I have also seen some use ArcGlass bedding compound from Brownells under the rear lug.

 

[rcmodel]

Someone here mentioned one of those coming loose and getting wedged in the FCG, resulting in a major malfunction.

Some folks put the Accu-Wedge in upside down and that won't work.
SO they start whittling on it with a pocket knife to make it fit.
Then it falls out & ties up the gun!

There is no possible way for one to fall out if you put it in the right way.

To install correctly, the long end goes UP behind the rear Pin.
The short thick end is down under the pin against the lower floor.
It is totally captive when installed this way.

The only way it can come out is after the rear pin comes out.


rcmodel

 

[Rick1911]

Peen It

You can peen where the pivot pin goes on the lower and the lug on the rear of the upper. Just like with the rails on a 1911 the metal has to go somewhere so why not put it where you want it. I also cut off the back on my accu-wedge so it is a button for up pressure. Now the peening and lead weights it feels like a real rifle. I don't know if ti helps at the 600 yd line but it feels ooo so gooood!
Just my two cents
Rick