AR-15 Receiver Slop/Loose Fit?


Still 2 Many Choices!?
February 8, 2007, 11:07 AM
As I said in the now infamous ,"Sniper SKS" thread, I recently scoped my Bushmaster AR-15. I took it to the range and was getting beatiful groups of 1" or less at 100 yards, BUT after I started shooting more rounds I noticed wandering groups:banghead: . Grouping would either be super tight, or look like my AK at 50 yards:scrutiny: . Most groups were shot slow fire 3 rounds at a time, with time for the barrel to cool in between. The wind was very light, and I even waited for gusts to slow to a minimum before shooting. The ammo was 55 gr Winchester Q3131 out of a 1/9 twist barrel. With the iron sights I can group under an inch at 50yards all day if I do my part. Does the loose fit between my upper and lower some how effect the accuracy with a scope more than iron sights? When I look through the scope, I can feel the lower kind of wiggling below the scope, and since my cheek weld is there, I assume it would effect where the cross hairs are in relationship to my eye changing point of aim and impact.

The scope is a BSA 1/8" click at 100 yards, 4-16X40mm illuminated reticle type. If anybody has a cheap fix to get rid of the upper and lower receivers play/slop, please let me know. I was thinking about getting one of those little plastic things that you place at the back of the lower receiver that sits under the rear take down pin, but then saw that the front pivot pin wiggled too. I am going to the dollar store to try and find something to place between the receivers that will minimize the receiver play. All help appreciated...

Still 2 Many Choices!?

PS-Funny side note- My ,"ban era", Bushie A3 M4gery has a welded AK type muzzle brake and not the regular gas block, so mounting the scope to the upper receiver placed the scope directly in line with the front sight base. The guys at Academy that mounted it for me didn't think it would work that way, but I explained that with the magnification at or above 4X, the scope will focus beyond the sight base and the sight base will blurr out and not show up at all. Sure enough, I was right:) .

If you enjoyed reading about "AR-15 Receiver Slop/Loose Fit?" here in archive, you'll LOVE our community. Come join today for the full version!
February 8, 2007, 11:27 AM
Try this O ring trick by Larry Medler........

Click Here (

Still 2 Many Choices!?
February 8, 2007, 12:01 PM
Just the kind of thing I was looking for thanx...Now I have to go to the store and get some more ammo and see what comes of this:) .

February 8, 2007, 12:35 PM
My take on it is that the sights are attached to the upper, which is attached to the barrel, and all stay in alignment the same way, no matter if there's a tight fit between upper and lower or a slightly loose fit. I'm on the side that a tight AR is more of a "shooter feel good" thing than anything else. Others will agree or disagree.

At any rate, my first choice would be to simply switch ammo. 55gr FMJ ammo of any kind ain't exactly perfect. I used to load those Win 55gr FMJs for practice ammo and quit because of inconsistent groups. One would be really nice and tight for 4-5 rounds, then whamo! Fliers. Frustrating.

So, in short, I recommend better ammo to start with and see if that improves your consistency. Dig up some 69gr Federal Gold Medal, or some Black Hills remanned 68gr or 52gr Hornadys. Then report back! ;)

PS: My match AR wiggles a little and I've never noticed the play to have enough influence on my groups out to 600 yards to matter. There much, much more wiggle behind the buttplate! :scrutiny:

February 8, 2007, 02:11 PM
My experience has been that the fit of the upper to the lower has no effect whatsoever on accuracy, assuming that the "slop" is not so egregious as to prohibit reliable function.


Still 2 Many Choices!?
February 8, 2007, 02:21 PM
With iron sights I beleive the slop does not have a great enough effect on accuracy to be noticed. Like I said I can keep around 1/2" groups iron sighted at 50 yards easily. The problem seems to come in with the scope being mounted to the upper and my cheek being rested on the stock which seems to change my relationship to the crosshairs because both the front and rear pivot pins allow for movement...

February 8, 2007, 04:05 PM
Bushmaster is notorious for loose fitting receivers. It bugs me.

February 8, 2007, 04:11 PM
Get an Accu-Wedge. Will tighten the upper and lower fit.

Thin Black Line
February 8, 2007, 04:13 PM
I've always used an accu-wedge, including on already tight fits. If it's
particularly bad, I'll use the wedge and the o-ring.

February 8, 2007, 04:14 PM
Zullo, that's a cool trick. I'm going to try that on a sloppy gun.

February 8, 2007, 06:00 PM
You have a link to the specific scope you've got?

I've noticed a similar affect on a RRA flattop while using a Leapers 4x20 scope. I don't know if it's similar. This specific scope came in two parts: the scope itself, and the scoup mount. The scope attached to the mount using a single tension screw, and while tight I could shoot about 1/2-3/4" groups without a problem at 100 yards using WWB. However, it has the perpensity to come loose, and not discernably so for the first 50 rounds after tightening. I used a pair of needle nose pliars in conjunction with some locktite and it's fine now.

I've also heard that the crosshairs in some cheap scopes have the perpensity to wander a bit or otherwise become loose. I don't know how valid that claim is.

February 8, 2007, 11:54 PM
I am with Caimlas. If it shoots consistent with irons and erratic with the scope, I'd blame the scope or the mount. Especially if it started out good and degraded. Is everything tight?

February 9, 2007, 02:58 AM
I'm Really not trying to offend anyone, But probly will. The scopes mentioned above are junk. they will not hold POA with any resonable expectation. But wait it only gets worse and all the -O- rings and and wedges will not make it better.
You have a great rifle, treat it to a good scope.

Thin Black Line
February 9, 2007, 10:16 AM
I've also heard that the crosshairs in some cheap scopes have the perpensity to wander a bit or otherwise become loose. I don't know how valid that claim is.

This can happen in more expensive scopes as well, but the more common
problem as you already mentioned are loose mounts/rings.

The scopes mentioned above are junk.

Just to be fair to BSA, I've had a similar scope survive a few hundred rds
on an HK91 clone. But I've had other scopes, both cheap cr@p that didn't
last two mags and quality name brand that lasted only a couple hundred
rounds before they gave out on an FAL. Funny thing is one of the cheapie
scopes had lasted at least 1,000 rds on an SKS, but died immediately on the
FAL. The FAL is now an iron-site only weapon since it appears to eat scopes
as well as it does ammo. That's even with one of those buffers in it.

Still 2 Many Choices!?
February 9, 2007, 01:02 PM
I am heading to the range on my luch break with a cheap fix just to check the scope out until I can find a more permanent fix... I will report back with the findings:scrutiny: ...

Zak Smith
February 9, 2007, 02:36 PM
Loose lower/upper fit is not a problem.

I have shot sub-1/2 MOA groups with rifles that had considerable upper/lower play.

February 9, 2007, 03:14 PM
I've not had accuracy problems either with a sloppy gun, but just as a personal note, I hate the wiggle.

February 9, 2007, 03:46 PM
I've not had accuracy problems either with a sloppy gun, but just as a personal note, I hate the wiggle.

AMEN! I can't stand it, I have found the o-ring trick works exceptionally well.:)

February 9, 2007, 03:47 PM
it just so happens that my RRA guns are tighter than i can describe on the high road.

however, i see it mostly as a downside because 90% of my shooting is suppressed and i'm lefthanded and i get a TON of gas back through the charging handle.

my face is normally half-black when i leave the range.

February 9, 2007, 03:55 PM
taliv, I shoot a lot of supressed too. I absolutely love the PRI gas buster. It really is worth the money.

Otherwise caulking your charging handle is supposed to work really good too.

February 9, 2007, 04:28 PM
that's why i mentioned i'm left handed... gasbuster is right-hand only

Still 2 Many Choices!?
February 9, 2007, 09:22 PM
Well I went to Wally World and bought up almost 70 bucks of Remington 55gr FMJ ammo, wich came to only 200 rounds:what: ! Then I decided to try a poor mans fix since I couldn't find a hardware store near the range, and Wally World had no "o rings". I decided to cut a normal office rubber band into a few small pieces and proceeded to place them on either side of the receiver just in front of the magazine well and ond near the back, wich wedged them in once the receivers were closed. The wiggle became non-existent.

After that, I proceeded to locking in the mechanical zero for Winchester(for easy resetting since that's my normal ammo), then zeroed the scope to Remington... Results were a 4 shot group I could cover with a quarter, and 1 flier that happened to be the first round out of the barrel:D . The group I shot before that one was a vertically strung 3 shot group that I didn't measure but was probably just outside 1 moa. This scope kicks butt!! The rubberband pieces took out all the slop, and didn't cost me a thing:) .

Now I just have to decide how to permanently mount them in there. Again, any ideas are appreciated, as I was simply thinking glue would do the trick.

I don't know if the slop was affecting the accuracy, but as the saying goes, If it ain't broke don't fix it(or as in the case, If it is fixed, don't break it again:scrutiny: )!

Still 2 Many Choices!?

PS- I have to work tommorrow, but will post a pic of the scoped rifle, targets, and rubberband pieces sometime Sunday.

February 13, 2007, 10:41 AM
I would caution you against using a rubber band. They are not well made at all and will break down fairly quickly, leaving shreds of rubber in your receiver. Also, rubber bands are quickly weakened by contact with gun cleaning solvents. If you like the tight fit and think it makes a difference in the accuracy of your setup, then I would recommend the accu-wedge. It's made of a stronger compound than rubber bands are made of and will stand up to cleaning chemicals. It's also removable and is much less likely to come apart in your receiver. I wouldn't want to glue anything inside of an AR's receiver.


Still 2 Many Choices!?
February 14, 2007, 11:09 AM
I am going to get a better grade of rubber for this but I still think that I will require something besides just the accu wedge to cure the front pin slop...

February 14, 2007, 11:36 AM
Ah hell, if you wanna talk about slop you should have seen the A2 I had to qualify with on PI. The thing looked like it was bead blasted stainless and was loose as heck. The extractor pin even managed to shear during the 300 rapid fire. It still managed to do 10 for 10 at the 500.

Still 2 Many Choices!?
February 23, 2007, 12:39 PM
This 5 shot group was shot with my stock 14.5" heavy barreled Bushmaster with AK brake and surefire rail(not free floated), using 55gr Remington FMJ off of sand bags at 100 yards... The "flier" was the first shot, and I knew I threw it low:o. The rest of it was the outcome after I slowed down. Not bad after I got rid of the slop, but from what I hear from you guys, it really shouldn't make too much of a difference...

Still 2 Many Choices!?

December 31, 2011, 01:37 PM
Try a #7 O-ring on the front pivot lug.

December 31, 2011, 02:00 PM
Uhh... Welcome to THR...?

For your first post you dug up an already-resolved 4 year old topic? (Also, your suggestion was exactly covered in the first response to the thread.)

If you enjoyed reading about "AR-15 Receiver Slop/Loose Fit?" here in archive, you'll LOVE our community. Come join today for the full version!