AR15 - Play between upper and lower


November 10, 2008, 08:53 AM
Just purchased an S&W MP15

I was wondering how much play there should be between the upper and lower.

I can see light between the upper and lower when looked at from the side.

Also, i can wobble the upper slightly against the lower.

Is this normal?


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November 10, 2008, 09:13 AM
It sounds like the play between your upper and lower is totally normal. If it really bothers you then you can put a accuwedge in it but it's not neccessary.

Thin Black Line
November 10, 2008, 09:25 AM
Accuracy improves when there is less play between upper and lower, but not
enough for most shooters to even notice. The accuwedge will help. Some
other company also makes a replacement rear take down pin that works by
adding pressure through the pin-hole itself. However, this requires some
additional tools/time to take the weapon apart.

November 10, 2008, 09:55 AM
I purchased the rifle complete.

I just wanted to be sure this was normal and not a defect I should send the rifle back for.

So its normal to have a little wobble between the upper and lower if manipulated in opposite directions?

Does yours do this?

November 10, 2008, 10:18 AM
Yes, perfectly normal. It's the nature of the beast.

November 10, 2008, 11:48 AM
It's normal, no worries.

Also, you're supposed to check that sort of stuff before you pay for it ;).

November 10, 2008, 01:59 PM
You also might check on these.

I would not recommend them for a combat rifle, but for target work it should tighten up the play.

Austin, Texas

November 10, 2008, 04:24 PM
A little play between the receivers is perfectly fine for function.

November 10, 2008, 04:33 PM
My RRA has so little play that before I hit 500 rounds she didn't even want to come apart with the pins out. I don't know about S&W though.

November 10, 2008, 04:36 PM
A curious phenoma for the AR15's is that tightness, so critical for accuracy in a bolt rifle, makes absolutely no difference in an AR.

These things can rattle and shoot tight groups.

What is the most critical is the quality of the barrel, and quality of the bullet. Assuming the sights are mechanically tight.

A friend of mine, who was listed as one of the top 200 high power shooters in the Nation, you could rotate his lower an incredible amount around his upper.

What made the difference was his Kreiger barrel, Malazzo trigger, and his skill.

I prefer a tight fit, use accuwedges. But it is a preference, not an accuracy requirement.

November 10, 2008, 05:11 PM
same with mine. slight play. I see like half a milimeter of light as well passing thru spacing by the rear take down pin. i ended up getting an accuwedge but there was still a slight play by the front pivot. but overall its a bit more solid now.

November 10, 2008, 05:16 PM
I would not recommend a wedge style take-down pin, as if over-tightened, you can crack a lower or upper pin hole.

I really do like the little rubber Accu-Wedge though. It not only takes all the slack out, but makes the gun sound & feel solid, like a bank vualt door.

November 10, 2008, 07:35 PM
I took a trip to the gun store.

I handled the MP15 they had there along with the Bushmaster.

That Bushmaster was TIGHT compared to both their MP15 and my MP15.

I can rock my upper back and forth slightly....but that Bushmaster wouldn't budge.

Makes me think the MP15 is of lower quality (rickety)

I will be firing it for first time this week...probably wednesday....but already i am unhappy with the movement in the upper

November 10, 2008, 07:38 PM
I guess I got lucky. My M&P15 is so tight I used to have use a pick or flat head screw driver to remove the pins. After several disassemblies it's much better but there is still no play between the upper and lower when locked together.

November 10, 2008, 08:06 PM
Maybe you got yours while Stag was making them.

Both MP15's I have handled had the same play.

I can move my upper about a centimeter while the lower is stationary. It just seems like it should be more tight than it is.

Anyone else have a loose MP15???

November 10, 2008, 08:22 PM
my m&p 15a has SN 61,xxx and it is very tight, yet not too tight were i couldnt use my thumbs to push out the pins. On the other hand the two bushmasters I held at the store seemed as if you could almost jam an oreo between the upper and the lower. ok, maybe i exaggerated that a bit:evil: but you get the idea. to you guys with the smiths with the loose upper to lower fit, what serial numbers are they?

November 10, 2008, 08:22 PM
whoa... with your gun fully assembled, both takedown pins in place, you can move you gun a Centimeter?!?!

maybe lets see some pics if something looks odd

cracked butt
November 10, 2008, 08:25 PM
How tight the receivers fit makes no difference-zilch- when it comes to accuracy. If the rifle starts out tight, it will eventually loosen with wear anyway.

November 10, 2008, 08:30 PM
cracked butt is right. mine is still tight, but it has loosened after use a little bit. i wouldnt worry too much about the wobble

November 10, 2008, 08:32 PM
My SN is 80***

Maybe I could upload a video to youtube and get a better opinion from yall

November 10, 2008, 08:42 PM
I have a Bushy that was loose as a goose. I dont know if its just a coincidence, but its also been the least accurate AR I've owned.

I tried the Accu Wedge, and it wasnt big enough, so I made one out of a drafting eraser that was, and solved some of the wiggle. I then went to the "O" ring on the front lug fix, and that got things solid. No more wiggle.

Its still my least accurate AR, but at least now, it doesnt bug me as bad.

November 10, 2008, 08:56 PM
Accuwedges and anything else small, rubber/plastic and wedged into the innards of the gun are bad ideas if the gun is intended for "serious" use. They can (actually "will", but most guns don't see enough use for the inevitable to happen) come apart, and parts can migrate to places where they can tie up the gun. That's a quick fix if you're plinking, more of a PITA if you're hunting or competing, and could be fatal if you're fighting.


Howard Roark
November 10, 2008, 09:20 PM
The best way to eliminate play is to either bed the upper and lower or drill up throught the lower and tap into the upper using a screw to tighten them.

November 10, 2008, 09:26 PM
Makes me think the MP15 is of lower quality (rickety)

My buddies Colt was the loosest fitting AR that I've seen, no one calls them rickety

But it didn't have a centimeter of slop:eek: Maybe a millimeter:)

November 10, 2008, 09:36 PM
I can move my upper about a centimeter while the lower is stationary.

Are you sure about this? The thing shouldn't be together if it moves that much.

November 10, 2008, 10:05 PM
the rifle wouldnt function properly if there is a centimeter of movement. maybe a millimeter??

November 10, 2008, 11:59 PM
Centimeter may be a slight exaggeration.

It moves back and forth noticeably though...otherwise I would not have recognized it

I just hope it doesn't give me problems with the guns accuracy.

Otherwise, I'll have to send a new $1200 gun back to S&W and that just blows :banghead:

November 11, 2008, 02:09 AM
My mp15 is relatively loose too, doesn't seem to effect it noticebly though.

November 11, 2008, 07:16 AM
I just hope it doesn't give me problems with the guns accuracy.
Even if it did, most people can't shoot well enough to tell the difference anyway.

Not that this is (necessarily) the case here, but I find it somewhat humorous in a lot of these cases where guys are worried about lower/upper wobble affecting their accuracy, and then go out and shoot 55 grain Wolf at 25 yards with a 4 MOA red dot sight. I guarantee, if that's the case, that the wobble is NOT the problem.

November 11, 2008, 11:26 AM
Here's why it doesn't matter.

Everything affecting where the bullet goes is on the same side of the divide. That is, everything is on the upper. The rear sight, the front sight, the barrel, the chamber...everything that impacts accuracy is in one solid piece. The only way you'll get inaccuracy from the upper/lower slop is if you can feel the slop and see the sights shifting while you are aiming. Your cheek is pressed against the stock, which is part of the lower, so play can come into the equation there, but try it a few times and be honest about whether or not it does. I've shot ARs that have some play, but I've never noticed the play while obtaining the sight picture and breaking the shot, because you're gripping the gun and pressing the upper down against the lower. You tend to notice slop when the gun is being handled or moved around, not when you're locked in for a shot.


November 11, 2008, 12:30 PM
90% of the time it's a non-issue. I was actually glad when mine loosened up, as I did not need something to push the pins out anymore.

Howard Roark
November 11, 2008, 04:48 PM
Here's why is does matter.

What happens when there is 10 to 20 thou movememnt between the halves and sometime between when the trigger is pulled and the bullet leaves the barrel the upper moves as much? Say it doesn't move one shot, the next shot it moves the full value or various amounts in between. Maybe this is part of why some say an AR can't be as accurate as a bolt gun.

It's the same as loose action screws on a bolt gun.

November 11, 2008, 05:41 PM
Quote by FMF:
"I guess I got lucky. My M&P15 is so tight I used to have use a pick or flat head screw driver to remove the pins. After several disassemblies it's much better but there is still no play between the upper and lower when locked together."

+1, Same here.........7x,xxx
Mine's as tight as a movement...Awesome rifle!!!

Hey kostarae, I'll bet it shoots fine...Let us know how it does at the range...Good luck...:)

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