Ar bedding help please

[russkim04]

I measured .0075 between barrel extension o.d. and receiver i.d.

Can you plz describe best way to get most accurate upper... I've heard of loctite and shims, heat and cold. Plz tell me your secret

 

[Makinchips208]

I measured .0075 between barrel extension o.d. and receiver i.d.

Can you plz describe best way to get most accurate upper... I've heard of loctite and shims, heat and cold. Plz tell me your secret

A high quality barrel will give a more accurate upper, typically.
If you have that much play then I believe one of the parts (barrel extension od and/or receiver id) is out of spec. Maybe replace the out of spec part if you are that concerned with max performance.
I have used green lock tight, but it’s not conducive to easy removal. And didn’t seem to improve accuracy, *for me, in my rifles, in my experience.

 

[Rocketvapor]

What are you using to measure I.D. of receiver?
Post your measurements of I.D. and O.D.
I have NEVER-EVER seen 0.0075" clearance.
A thin strip of paper or tune up feeler gages could prove out your clearance.
AR-15 upper bore diameter is spec'd @ 1.000" +/-0.002".
AR-15 extension is spec'd @ 0.998" -0.0008, + 0.
If you were "Lucky" enough to get a bore at the MAX spec, and an extension at MIN spec, that would be 0.005" or so.

Soft shimming with Locktite could allow the extension to sag to one side or even set in crooked if receiver face is not square.
Hard shimming would center extension better.

 

[russkim04]

What are you using to measure I.D. of receiver?
Post your measurements of I.D. and O.D.
I have NEVER-EVER seen 0.0075" clearance.
A thin strip of paper or tune up feeler gages could prove out your clearance.
AR-15 upper bore diameter is spec'd @ 1.000" +/-0.002".
AR-15 extension is spec'd @ 0.998" -0.0008, + 0.
If you were "Lucky" enough to get a bore at the MAX spec, and an extension at MIN spec, that would be 0.005" or so.

Soft shimming with Locktite could allow the extension to sag to one side or even set in crooked if receiver face is not square.
Hard shimming would center extension better.

I'm working with ar10. Extension is 1.185 dia and bore is 1.1925 ish.... machinist by trade using mitutoyo dial calipers in like new condition. Yes i know its not super accurate like a dial bore gauge and o.d. mic..... but barrel sure does rock around allot and my accuracy won't repeat.

So it sounds like i should just skip the loctite and maybe gently heat receiver and work barrel into with prob a .001 or .002 shim? Maybe easier to break apart if after all this i still see the barrel is junk and i have to pull out and toss in the trash....

I also ordered a lapping tool for face, so that will be done too

 

[Rocketvapor]

I went back and looked at your previous posts and see that you are an AR-10 guy, sorry for the info on the AR-15.
The extension diameter I found was 1.188" but no spec.
If it rocks in the bore your measurements are likely good.

My procedure for an AR-15 is to lap the face (Wheeler tool) and measure bore with this:
Cheap Chinese ($53) inside mic that checks very close to 0.9985" X master.
Would of course need another ring for AR-10 bore.

I checked one upper at three depths from the nose @ 0, 60,120 degrees. Got about 0.0003" under an inch.

My extension has a slight taper and almost slides all the way in.

Now, where I do things a little differently is shimming.
I use a spray on shim (high heat engine/Bar-B-Q paint) burnished smooth. For 1 or 2 thou getting it on evenly is easy peasy. Maybe your gap is too much for this method. Steel shims would probably be better for the gap you have. Blue or green goo would be hard to end up with the assembly centered.

The receiver goes into the oven @ about 220F, barrel stands up in freezer @ about 4F. Slap together and hand tighten nut and wait.
Aluminum and steel will remain a "Thermal" fit even at pew pew pew temperatures

 

[russkim04]

Ty to All.....i ended up at.003" shim wrapped around extention. I was able to push in about half then used a Torch to get rest in