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Question for AR Guru's , play between upper & lower

At the range last week trying a new scope, I sighted in then moved to 300 and started noticing patterns and not groups. I checked the scope and it was secure BUT there is what looks like the thickness on a sheet of note book paper "play" between the upper & lower on my Armalite AR-10 .

I didn't notice this two weeks ago ?? Any thoughts or suggestions ?
 
Put a #21 o-ring on the front lug. It will take the slop out and works better then the rubber wedge.

Here is a link to a video showing how to do it https://m.youtube.com/watch?v=We4iLuvkVB0
 
You lower may have tension screw. You'd find it under the rear lug. IF it has one remove the rear grip and snug it up to eliminate the movement. If not the accu-wedge works under the rear lug.
 
Yeah, and that crapuwedge will also make your holes oblong, ruining your upper! Don't use em! I've seen ar s that rattle shoot tiny groups, look somewhere else first
 
Years ago I cut a paper card/poster board type sheet to fit in between, cut out the center too so parts could move.. worked great. Made a difference on paper too.
 
I use the shim below. I tried the wedge and it eventually collapsed and failed. I am sure they could make the hole oblong, but not as much as I shoot. I tried the o-ring on the front lug and it crushed and broke. Some people have used bedding compound and bedded the upper to the lower, but that seems like too much work for me.

I just take the time to fit the National Match Shim and it works great. He sends emery paper with it. I don't know if it will fit an AR 10, but if it does it will serve you well.

http://proattach.com/nationalmatchshim.htm
 
I believe that slop comes from not lubing the pins holding the top and lower together. When I get a upper/lower that are loose, I have in the past, gone to hobbie lobby and bought a piece of brass shim in 5 and 10 thou. Cut it so it will sit behind the hammer far enough to clear when it cycles. Cut it long enough that you can bend the ends over. This will keep it from drifting. Works for me. Another fix is to drill and tap for a screw/bolt to adjust as mentioned above.
 
I ‘bed’ an upper to the lower it’ll be used with most often, using JB Weld. Easy enough to do!

BUT be sure to use parting fluid (CLP is effective, or any kind of not-too-thickish oil or paste wax) on the corresponding surfaces of your lower before setting the assembly up for full cure period. You want the upper bedded, not permanently attached....

I hang mine from the barrel, using a barrel vise at the edge of bench and hand grip straight down, with the buttstock off. Weight of the lower alone is enough to maximize the gap the JB is intended to fill without adding an unneeded bending moment.
 
Wow! So this thread from Almost two years ago gets drudged up by new guy Ricky1... who is asking for something not related to the topic then the thread gets piled on by a bunch of home remedies..... Wowser.
 

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