I've been asked time and again from newbies to the AR15/M4 platform about the "wiggle" or knocking between the upper and lower reciever of the AR series of commercial and military grade rifles.

1. It's not a conern unless your rifle is so loose that your MOA is affected by anymore than .5 MOA @ 100 meters. Generally speaking if your rifle is slung your going take the creep out of the upper and lower once you present the weapon, into your shoulder, cheek tight on your target.

2. Tolerance staking is alway's going to leave a bit of play between your upper and lower. Yes, sometimes you might get an upper and lower that are fairly tight. The recievers are like anything else being manufactured under mil spec dementions. They are not all going to be perfectly hand fitted to emlinate the wobble between the upper and lower. Imagine cutting two x Fours ? If you match them up, they are not all going to to exacting specifications are they ?

3. You can if desired send the rifle back and have them hand fit the take down pin and the pivot pin to exacting standards. However you may wind up with rifle that is only designated for that particular upper. If you change out for another upper it probably is not going to fit. Be carefull before making this decision.

4. If you've got to scratch that itch and can't stand the rifle "wiggle" then I suggest using two items that are inexpensive to scratch that itch.

A. AccuWedge- Can be found online for about $3-$5 dollars. Simply push into the low shelf where your takedown pin is located and it tightens up the wobble. You may have to use a razor blade or sharp knife to trim some off the bottom to actually get the upper and lower to close tightly and to push your takedown pin fully into place. It's an easy install without the need for any gunsmilth or tools.

B. If the wiggle, wobble still occurs then use an "O" ring on the front hinge/lug. These can be found at just about any hardware store. the proper size is 5/8 x 1/2 x 1/16 Although I have used the slighly
larger 1/2 x 3/8 x 1/16 If you use the former, it will take some strong depression of the upper to the lower to achieve the pivot pin to it's full closure. I rec' the 1/2 x 3.8 x 1/16. This will eliminate all wiggle/wobble and only cost your about $6 total before spending money on such things as larger pivots pins and the cost of having your rifle sent back to the manufaturer to scratch that itch.

Their usually found in the plumbing parts supply section of Lowes or wherever you do hardware shopping. The brand name that I have purchased recently for a team is Danco.

Hope that helps if any of you AR enthusiast haven't figured this out or heard of it before.

Cheers,
Ropadope