Should there be any rocking movement between the upper and lower of a M&P Sport?.
I seems that it is rocking on the receiver pins,could the pin holes in the upper receiver be too large?.

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Retired Plumber

Yes. There will always be some lateral play, wiggle, between the upper and lower receiver. My 15-Sport has the same little wiggle. My home built AR is just starting to get a little wiggle. Personally, the little wobble never bothered me. More importantly, it hasn't negatively affected my accuracy.

There are aftermarket doo-dads that will supposedly fix the wobble, the Accu-Wedge comes to mind. Some people make their own washers to wedge between where the upper and lower mate. Few take the extreme of applying epoxy or JB weld and shaping it.

Another quick and simple fix is to go get a few rubber O-rings of appropriate diameter. Wrap the O-Ring around the front pivot pin opening on the upper... let me google up a pic...



Not my pic, but this is what you do. The trick is to try out a few different thicknesses of O-rings.

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-John

The movement has absolutely no affect on accuracy. My service match rifle rattles but still shoots sub 1/2" groups off the bench.

Use an O'ring like John suggests if the movement bothers you.

ERGO ACCU-Wedge-Fixes AR-15 Upper & Lower Slop - 4988

I've never used these, but I have heard that they can break down with use and little bits get down into the trigger group. Have no idea how long this takes, just read it on the 'net so it must be true...

you've never used them, I've never used them....neither of us are qualified to give an opinion either way! I was just throwing out options....research is your friend.

I have read the ERGO ACCU-Wedge will not work in the M&P 15 AR. Even if you shave them down. I did my research but can not seem to find where I found it to prove I am not wrong.

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NRA member since 1974

I have the accu wedge thingy. It does exactly what it says it will do; makes the fit between the upper and lower tight. Mine has not broken down and no small pieces have come off it.

I just don't think that a little movement is really a problem.

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Freedom isn't free.

I tried one, they are so inexpensive I figured what the heck. For a S&W, you pretty much wind up removing 90% of it. It worked, but I tossed it. Spent more time trimming it down than it spent in the rifle, actually lol. I'd suggest the o-ring on the front lug if one is really bothered by the wiggle/rattle.

I also had an Accu-Wedge on the AR I had before my Sport. The wedge helped, but that AR was pretty loose, not very well built, and I eventually traded it away. As far as the wedge itself, I had no problems with the wedge breaking down and it did tighten up the upper/lower fit. Frankly, wedges are cheap enough you can pick up several to keep on hand if you're worried about wear. JaPes's O-ring looks like a good, less expensive, solution also.

Personally I like the O-ring solution too.

One thing I found with the Accu-Wedge is that it didn't change my accuracy any. Of course, that's probably more due to the shooter than anything else. I don't think a little wiggle is a problem. I could see how a lot of wiggle could cause issues though.

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Freedom isn't free.

I have one of the Accu-wedge style doo-dads in my Armalite. Like others mentioned, I had to shave most of it away to make it fit. It tightened things right up and I have not had any problems with it breaking down. I assume it is made of an oil-resistant rubber, so unless it is exposed to direct sunlight, I don't think it will break down for a long, long time. I have heard that it will ever-so-slightly improve accuracy; the theory being that you want your platform as stable and repeatable as possible. I don't know if I am good enough to see such an incremental improvement but it was only a couple of bucks.

The wiggle took me some getting used to on ARs--I bought o rings, washers, and accuwedges--because rifles should not wiggle betwixt their parts, right?

Well, none of those things really matter or make any difference. I don't use any of them anymore. I'm no expert shot, but I can keep all my shots on a 8.5" square paper, using iron sights at 100 yards, and the wiggle doesn't seem to hurt anything.

I used the o-ring on mine. If you're wanting to try it you will need a #41 o-ring.


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Good info to know - I might try that method, too!