Shimming and bedding a barrel

C

Coyote-conquest

Active member
Im not sure if anyone has ever tested the results of whether shimming and bedding a barrel really works. Ive read about it with people saying both ways. Im not big on it because it can be a pain in the you know what if you have to remove the barrel for any reason. I did it one time before but I had never shot the barrel any other way. I did end up have to pull the barrel to have it chopped and rethreaded. It sucked.
Anyway I have a 223 wylde barrel that I was really close to selling because it just didnt shoot very well. It had always been around 1.5" and it wasnt a cheap barrel. It sits in a BCA side charging upper so not the best but I dont find them bad. (I use BCM for most builds)As a last resort before selling it I decided to shim it and bed it to see if it helped. I had some .001 stainless shim stock and some loctite 609 sitting around from the last time I did it. It couldve maybe took a .002 or bigger shim but the .001 was all I had and I wasnt about to try to double it.
I pulled it all apart, verified I had lapped the upper before I assembled it the first time then shimmed it and bedded it. I let it sit for around 24 hours.
I was really surprised how much it helped. It shoots right under an inch for 5 shots. I shot a 1.3" 10 shot group.
Ill try to stick with BCM just because the thermal fit but its something ill always keep in mind. Im not saying it will help with every barrel but it definitely helped with this one.
 
Thx for sharing. Ive heard of the loctite trick, and understand it, buy never heard of shimming barrels? Have to read up on that one.
 
Coyote-conquest said:
Im not sure if anyone has ever tested the results of whether shimming and bedding a barrel really works. Ive read about it with people saying both ways. Im not big on it because it can be a pain in the you know what if you have to remove the barrel for any reason. I did it one time before but I had never shot the barrel any other way. I did end up have to pull the barrel to have it chopped and rethreaded. It sucked.
Anyway I have a 223 wylde barrel that I was really close to selling because it just didnt shoot very well. It had always been around 1.5" and it wasnt a cheap barrel. It sits in a BCA side charging upper so not the best but I dont find them bad. (I use BCM for most builds)As a last resort before selling it I decided to shim it and bed it to see if it helped. I had some .001 stainless shim stock and some loctite 609 sitting around from the last time I did it. It couldve maybe took a .002 or bigger shim but the .001 was all I had and I wasnt about to try to double it.
I pulled it all apart, verified I had lapped the upper before I assembled it the first time then shimmed it and bedded it. I let it sit for around 24 hours.
I was really surprised how much it helped. It shoots right under an inch for 5 shots. I shot a 1.3" 10 shot group.
Ill try to stick with BCM just because the thermal fit but its something ill always keep in mind. Im not saying it will help with every barrel but it definitely helped with this one.
Click to expand...

I have a couple BCA uppers and BCA they always sloppy as hell on the fit on the AR barrel shanks. Bedding is a must if you want them to tighten up the groups. If your NOT using a rubber mallet to set your barrel in the upper then it to loose . I use Permatex Sleeve Retainer and they always shoot better groups.
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I have SEVERAL DOZEN AR15 and AR10 precision oriented rifles... yes, several dozen.

Some have shim stock between the receiver and barrel extension whereas some do not. They all shoot under MOA with specific ammo as it relates to the specific rifle... that's to say they are not all sub-MOA with ANY ammo.

For me, bedding a barrel falls into the better to have than not have category, IMO odds are you will see a benefit but with a reasonable fit between the barrel extension and upper, along with proper barrel nut torque, absolute 100% results in the positive are iffy and not a guarantee.

I've posted many times here two 10-shot groups fired back to back with a 24" bull-barrel AR15 that had no special attention that are 1/2 MOA... yes, that's 1/2 MOA... that's NOT to say the rifle is a pure 1/2 MOA rifle because to call it that I'd have to be able to do all the time, every time. It usually shoots below 3/4 MOA, for a bone stock over the counter home brew I'd say that's pretty good.

In short, I bed not from an expectation standpoint but from an element elimination standpoint.
 
I've never done a 'before and after', but I've seen enough evidence to be a pretty firm believer in lapping receivers and bedding AR barrels. It's easy and cheap. Why not?
 
I put together a relatively expensive ultra light 6.8 SPC complete SBR build and when I got my barrel in I checked it with the upper receiver and there was too much play for me especially given the cost of the parts. I contacted the manufacturer of the billet receiver set and explained the problem to them and they said if I had the purchase receipt they would swap it for another receiver. They had me ship the barrel to them to verify the barrel was not out of spec and they sent me back a new receiver set that was nice and tight on the barrel extension.

My last build was a 22 ARC and I decided to go with a THERMAL FIT upper receiver and I was very pleased with how it turned out. That is probably the best way to guarantee a tight fit between the barrel extension and upper receiver.

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Centurion Arms AR-15 CM4 Forged 5.56 Stripped Thermal Fit Upper Receiver

Our forged upper receivers are a great complement to our forged lower receivers. The thermal fit inner dimension measures at .997 -0.0/+0.001″ and requires the application of heat in order to provide a solid mate to the recommended barrel extension. By heat we mean more than Granny’s hair...
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I've never used bedding on any of my upper builds..... I've just used rock set and set the torque on the nut to 65 ft/lbs. The tightest fit I had where I had to use a rubber mallet on top of heating the upper with a 1200* heat gun was my BCM upper to geissele barrel. That pair ain't never coming apart. None of my uppers are bad shooters
 
I'd bet using rokset on the barrel tenon is the ssme as bedding the barrel. It sets up and takes up any slop in the fit up.
 
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