How much wobble do you guys have between your upper and lower? I have a 14.5 BCM pinned to a PSA Lower and see a little wobble with a fully loaded mag in it. A buddy of mine has a DPMS with substantially more wobble. I've had a DD upper mounted to this lower once before and it had relatively none even without a magazine inserted.

Just curious, thanks.

I have from super tight to where I need a punch to even get the pins to disengage and one sloppy enough I could almost fit a credit card through the gap but, they've never given me any functional issues. It's never really bothered me though and I haven't once ever thought about putting an Accu-wedge in there. I did place an O-ring on the front lug and it definitely tightened it up snug but, after it eventually broke, I never bothered to replace it.

I'd never even heard of an accu wedge before, but I just bought one. Seems kind of chintzy but I'll give it a shot for $5

All of mine wiggle a bit.  It's not an issue.  Shoot and enjoy

What is bothersome obviously differs from person to person. It's hard to say what is a "little" since that might be "a lot" to another person.

My first AR build was with a BCM upper paired with a different brand lower. It was so tight that I had to tap the front pins in. I decided to take my front pin out and swap it with another pin, and suddenly it was extremely easy to assemble with hand pressure alone but it wobbles a little.

As you are aware it really has nothing to do with function. The accuracy of the rifle comes from the upper and so long as that is good, then you're good to go. There are some "room for error" when the bolt travels back into the buffer tube. It doesn't have to fit exactly into it. So it being off or something really has little effect.

The beauty of the AR15 is that it allows for play. The FSB is made a little larger so gas can travel back even when off centered a little. The gas tube wobbles a little so that the carrier can cycle correctly. Etc, etc, etc. Each manufacturer makes their parts a little different from the spec. Some go for slightly larger while others go for slightly smaller. Making all the pieces work together, especially buying cross brand, is going to be difficult and "luck of the draw" most of the time.

DPMS makes their stuff a little loose. They want their product to work with the widest ranges of other products. They want you to install a new trigger, they want you to install a new upper, they want you to get a new stock, they know you'll use crap ammo so they make it a bit gassy, etc, etc. BCM tries to follow that as well but tries to keep everything as mil-spec as possible to please their intended customers. So it's not as gassy, but it's a little looser to fit into the widest range of other parts, etc, etc.

Some wobble more than others, from no movement to full on rattling.  That's part of the reason I've been using Aero lowers with the tension screw lately.  Makes it easy to fix that problem.

I don't care because it isn't a problem.  I qualified several times with a wobbly M16 in the Marine Corps.  Most of those times, I shot Expert or Sharpshooter, barely having missed Expert by two or three points.

I hate wobble between receivers even though it is common. All my AR's are solid because I fix the wobble.
I will take pieces of rubber (rubber roof / inner tubes of different thickness) and cut small rectangle pieces to fit in the lower under the rear take down pin block. I adjust how much / many pieces of rubber to fit in place to make the receivers snug and then superglue the pieces into the lower. Snugging up the receivers means it will not be as easy to push the rear take down pin out but it is well worth it to me to have a solid connection between receivers. This works very well.

waste of money

you can bed the upper to the lower

wax lower where rear upper lug hits,

clean bottom of upper lug (brakeclean)

put a dab of epoxy on upper lug

close/put pin halfway through

let cure.


Now it wont move and you wont have loose junk in the gun

Since technically the lower has "no effect" on the accuracy of the rifle, a lot of people will say that wobble is unimportant.

Technically, that's right - about the rifle itself - but it doesn't take into account that the shooter plays a huge part in accuracy.  In other words, if you aren't comfortable with the rifle (whether it's upper/lower wobble, stock length, grip angle or anything else), you aren't going to be as accurate with it as you'd be if you were comfortable with it.

Most of my military M16 training and refresher training was at Lackland AFB, where all basic classes used the same rifles used by Basic Training trainees...  These are not safe queens by any means!  There were times when I could hear the lower rattle a bit on the upper, but in that setting, I was able to avoid the play getting in the way.  Maybe that's because it wasn't "my regular rifle," or maybe I was just paying more attention.

Most of the time, it's just a matter of manufacturing tolerances between different brands, usually just the precise dimensions of the upper's lugs and the lower's pockets.  But I did have an issue with play that was not due to the receivers themselves, it was due to a too-skinny pivot pin.  Took a bit of detective work to figure that out, but a new pin made a big difference.  Either way, if it bugs you, do something about it.

So simple and there's nothing to fall in to the action of your AR...

mk18 build has a decent amount of wobble.


knights armament sr15 has 0 wobble.



im not worried about the fit of the upper and lower together, never had any problems.

These o-rings snap.  A "fix" for a non issue.

I bought a full pack of these and tried one an an AR.  After three takedowns the ring snapped and fell into the AR.  Also, I've read reports where the tightness puts additional stress on the takedown holes and they "egg" out.  This makes the natural wobble even greater.

No thanks.

Works but the epoxy nub can fall off with heavy shooting as well.

Accuwege, epoxy, o-ring - they all can work.  I have had the best results with o-ring and accuwedge personally.

I have an accuwedge in my heaviest shooter and it has not broken down yet.

I have used o-ring in instance where accuwedge doest work well like a high shelf receiver...they work great but its pretty much replace every time you shoot then break down the gun.

My above post explains the proper way to eliminate wobble between receivers.
For those who want a quick easier way like an Accuwedge there is a cheaper alternative for this. In the tile section of your hardware store you will find plastic tile spacers shaped like a wedge. They can be cut a little bit to fit behind the take down pin block and work like an Accuwedge. You will find packs of 100 for a few dollars and they are actually stronger than an Accuwedge.
I would recommend just doing the proper and permanent fix though.

Both my AR rifles have wobble between the upper and lower. Its normal and does not bother me at all. One of my lowers has the tension screw to remove the play between upper and lower and I have never even used it.

if you do it correctly it wont

I have a dias that is bedded to many uppers-thousands and thousands of rounds.
at least 75K if you include the shrike.

I probably don't shoot as much as you though

Non issue for me. I don't believe it to effect accuracy much as the optic is mounted to the upper.

I don't do a whole lot of precision shooting with AR's anyways tho, TA31 at 600m is about as far as I ever take it, so take that for what its worth. But I've definitely never noticed any sort of con to receiver wobble before.

It obviously will affect accuracy. Anytime the rifle part that holds the sighting system is capable of having side-to-side movement (the upper half in this case) especially a 'flopping' action, your accuracy could be reduced by several MOA. The reason I installed Accuwedges in both my ARs is they both have optical sights - one a 4X ACOG and the other a MRO dot. Shooting off the bags without a hand on the hand guard or barrel, I noticed both 'flopping' after the shot which hindered a fast second shot. The proper way to use an Accuwedge is to fit it so it firms up the fit without forcing undue pressure to pin the action. Once fitted, the Accuwedge can't go anywhere or interfere with anything, and I have seen no degradation of the material or effectiveness in many years of use. You should have to put some weight on the rifle to pin the upper to the lower, but it doesn't take much. You use the rings around the bottom of the Accuwedge as a guide to take off very thin layers with a razor knife until you get the fit you want.
All I can say is after installing them I quickly got the groups I was looking for.

No kidding. They're also like 1 cent. Impossible for it to fall in to your AR since the front lug is on the OUTSIDE of the AR even when mounted to the lower. Inspect at each takedown and replace as necessary. Easy peasy.

:/ you win the sarcastic award today.  

Please give more detail on the proper way because I am having trouble understanding how a dab of epoxy is not going to chip off the rear lug with some recoil and use.

I've also read, as stated above, they put additional force on the takedown hole and start to egg the hole out.

No thanks.

I'm with you, how does it NOT affect accuracy if you're holding onto the lower, with your right hand, your cheek is on the stock tight, and your upper is flopping around left to right or what not.  obviously it's going to depend on the degree of sloppiness, but if it's there enough, I would think it could affect accuracy.  

I don't care much about dings, scratches, imperfections in the finish, etc, but I really don't like a sloppy fit.  Nothing more annoying to me than grabbing a handful of upper and it's moving around in a separate motion than the lower.  

My Colt A2 has an accuwedge and it solves it for that one.  On my recce the front lug is a bit small and will move in any lower.  I have used and o ring but if you go too big, it can affect function.  I use a paint pen and paint the sides of the lug whenever it needs it.   The other AR I have at present is plenty tight.  And I've had others that were plenty tight.

Do you have a vertical forward grip? If you don't, get one. Torque the pistol grip one way, and the VFG the other way, and - like magic - the wobble is gone.

My Colt lower is super tight on any upper and my BCM lower has some slight wobble. I am kinda disappointed with BCM because of this. Now I feel like all my future builds should be with Colt lowers lol.

Accuwedge did nothing for the wobble and made the takedown pin impossible to remove by hand, wasn't expecting a miracle from the product but it gave absolutely no enhancements, only negative changes.

It's not going to do a damn thing for accuracy unless you are trying to point shoot. Use your sights and it will be fine. The sights are on the upper, the barrel is on the upper, as long as the barrel and sights don't move, wobble between the upper and lower won't mean jack shit. Maybe, maybe, just maybe a tiny bit if you're trying to shoot national match states. For the people who aren't the top shooters in the nation it won't matter at all.

You are only considering the rifle part of the equation. If the lower moves around the connection to your shoulder and hand also will move around.
I don't think it will make a big difference unless the wobble is extreme but a shift between the body and gun could have some effect.
Although the upper and sights are all connected solid and are not effected by wobble your body is connected to the lower and body movement is important as well when accounting for accuracy.

I am not saying that someone can not be as accurate with wobble between their receivers. For bench rest shooting I can see that wobble would likely effect accuracy adversely. For all other shooting some wobble could actually help with accuracy because small movements in the body would not transfer to the upper as directly? If a rifle was designed with enough wobble (some kind of spring system between the receivers) body movement would not effect accuracy at all.  Someone could be dancing the Jig and still shoot accuratly as long as the arm holding onto the upper is stiff.
I am just making logical guesses like anyone else but wobble is irritating either way.

The maximum acceptable gap is 0.020", which you can measure by using a feeler gauge.  

Page 0021-21 of TM 9-1005-319-23&P actually has a set of procedures to check the gap between the upper and lower receiver which deals with lateral flex instead.
Figure 29. Use of Thickness Gage.

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 in. 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 or replacement of weapon is required.

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

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

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