Question about bedding a barrel with shim stock

[TheIceman93]

In the past, I just installed my barrel into my receiver, torqued it down and moved on. Then I started reading about bedding barrels with Green Loctite or shim stock to improve accuracy. So I decided to bed my barrel for my next build.

I'm using a CMT billet upper with a Daniel CHF barrel. The fit out of the box hasn't too loose but loose enough that precision guys would want to bed it. So I bought the thinnest shim stock I could find (.001) and cut a strip that wrapped around the barrel extension, stopping just shy of the ends of the shim touching. Well even after heating up the receiver with a blow torch, I could only get the barrel halfway into the receiver.

I guess even .001 stock was too thick. So I decided to cut the strip in half and place the now smaller strip on the underside of the barrel extension. I heated up the receiver again and the barrel slipped in. Once cooled, the barrel was locked in. No wobble, impossible to pull out by hand. Sounds like a perfect thermal fit.

Buy now my OCD kicks in and I start to wonder if it's a bad idea for accuracy to have shim stock that only wraps around the bottom 50% of the barrel extension circumference. Could uneven pressure from the shim cause any issues with the barrel accuracy potential? I'm probably being paranoid but I could only find pictures of shim stock wrapping completely around the barrel extension.

 

[Near miss]

Usually when bedding, more contact the better. But these things are not very straight-forward, please shoot it and report back.

 

[Dino11]

It doesn't have to wrap all the way around the barrel, or you could just glue it in with some loctite. I use the loctite method, and if it needs to be removed later a little heat and a wood dowel , hammer and it comes right out of the upper.

 

[S197]

In the past, I just installed my barrel into my receiver, torqued it down and moved on. Then I started reading about bedding barrels with Green Loctite or shim stock to improve accuracy. So I decided to bed my barrel for my next build.

I'm using a CMT billet upper with a Daniel CHF barrel. The fit out of the box hasn't too loose but loose enough that precision guys would want to bed it. So I bought the thinnest shim stock I could find (.001) and cut a strip that wrapped around the barrel extension, stopping just shy of the ends of the shim touching. Well even after heating up the receiver with a blow torch, I could only get the barrel halfway into the receiver.

I guess even .001 stock was too thick. So I decided to cut the strip in half and place the now smaller strip on the underside of the barrel extension. I heated up the receiver again and the barrel slipped in. Once cooled, the barrel was locked in. No wobble, impossible to pull out by hand. Sounds like a perfect thermal fit.

Buy now my OCD kicks in and I start to wonder if it's a bad idea for accuracy to have shim stock that only wraps around the bottom 50% of the barrel extension circumference. Could uneven pressure from the shim cause any issues with the barrel accuracy potential? I'm probably being paranoid but I could only find pictures of shim stock wrapping completely around the barrel extension.

If it will not seat with shim stock, just use loctite that is a retaining compound (600 series) not thread locker

 

[TheIceman93]

I found some .0005 shim stock. I'm going to give that a try. If that doesn't work, I'll go with high temp sleeve retainer.

 

[LRRPF52]

There is a fellow Hide member whose Iron Ridge Arms billet set was fitted with a Krieger 20” .308 barrel.

It was shooting 1.4"-1.6” 5rd groups at 100yds consistently in my hands, which wasn’t representative of the potential of these high-end components. Since I have owned and shot multiple AR-10s over the years and have consistently demonstrated the ability to group with the ones that would shoot, I knew some things could be done to tune-up the build.

I broke it down, replaced the eroded DPMS aluminum gas block with a steel unit, replaced the gas tube with an ArmaLite length since the gas system was cut for ArmaLite length (but advertised as DPMS length), de-edged/blended/polished the feed ramps, and bedded the barrel. I did my usual gas block and gas tube alignment work, and reassembled the rifle carefully, following my build spec approach.

First 5rd group out of the gate with the same 155gr SMK load was in the .6”s. With load development, I wouldn’t be surprised if that rifle could produce averages in the .4 MOA or better range for multiple 5rd groups.

I can take 2 identical rifles using all the same components, and by means of different assembly methods, produce entirely different results.

For yours, I’m leaning towards just bedding it with compound. Another approach I use is building the Cerakote up inside the barrel extension tunnel ID if the fit to the extension isn’t as tight as I would prefer. I make sure to not allow this build-up to occur inside the carrier raceway, because we’re not trying to create excessive coefficient of friction for the carrier rails inside the upper, especially on an AR-10.

 

[Yondering]

I found some .0005 shim stock. I'm going to give that a try. If that doesn't work, I'll go with high temp sleeve retainer.

I wouldn’t use .0005” stock with what you’ve described.

If the barrel is a loose fit without any shims, you should be able to make it work with a full wrap of .001” shim. That’s a .002” press fit at the most, and more likely closer to .001” (if it feels loose, you’re not starting with a perfect fit).

A .001” press or thermo fit is just about perfect, so I suggest trying that again. Maybe leave a little more gap between the shim ends, cut the corners to clear the pin, and make sure there are no wrinkles. If you already did all that the first time, then you probably need to use a little more heat, and/or tap the receiver home with a rubber mallet.

If you get the barrel seated far enough to start the pin in the slot, you can let the barrel nut seat it the rest of the way.

Edit to add - you could just use sleeve retainer compound like some said, and I’ve done plenty of that myself; it’s the easy way but it’s not as good as a solid press fit with shims. Just depends on the level of precision you’re trying for.

 

[cellular]

i dont know much about bedding, and you sound like u got it under control for now, but as far as shim stock if you cant find thickness you want in the future, buying a set or two of feeler guages can work. you will then have multiple thicknesses you can work with. the thinnest usually being about a "thou and a half though", from what i bought

 

[Yondering]

i dont know much about bedding, and you sound like u got it under control for now, but as far as shim stock if you cant find thickness you want in the future, buying a set or two of feeler guages can work. you will then have multiple thicknesses you can work with. the thinnest usually being about a "thou and a half though", from what i bought

That works for some other uses of shim stock, but you really want a wider section of shim for AR barrel bedding than a feeler gauge.

McMaster Carr sells a good selection of shim stock and it's fairly inexpensive. You can buy an assortment pack that has all the sizes you're likely to need.