How do you bed a barrel to the upper receiver?

[Huckleberry75]

How do you go about bedding a barrel to the upper receiver? I bed my own bolt guns, but am new to accurizing AR platforms. Thanks in advance for any tips.

[A5BLASTER]

Lather the extention down with locktite install, torque it down then clean up the locktite that squeezed out.

Lapping the recover is always a good idea as well.

I like to bed with steel shim stock now, I use a thickness just a bit to thick to fit then heat the upper so it expands and then install barrel, then let cool for a very tight compression fit and then torque it down and enjoy.

The steel shim stock can be found at hardware stores and online in small rolls and different thickness.

[centerfire]

It depends on the barrel and receiver fit up. I used blue loctite on my Grendel because it already had a tight interference fit. The last AR10 I built had a loose fit up so I used Indian Head. Indian Head is thick and will take up more space.

[rebby]

I wonder if the "Indian Head" that centerfire referred to above is similar to Loctite Green 620? I use the 620 on all my builds (in addition to lapping the receiver) unless things are really lose. If getting a new upper isn't an option, I'll use a combination of steel shims and the 620 for a really bad barrel/upper fit. 620 is really good stuff and it can fill a gap up to 0.015" (in theory you could be as loose as 0.030" then). It's also good to much higher temperatures than the standard blue/red options and holds up to some pretty harsh chemicals (like acetone, ATF, brake fluid, motor oils, etc).

If you have a lathe, you can always build up the barrel extension with a high temperature, high strength, steel reinforced epoxy (like JB Weld, although I'm sure that there are better alternatives). Once it cures, just turn the extension down until it almost fits then heat the receiver and slide it home. When the receiver cools, it'll be locked together pretty good. The only downside to this method is that unless the barrel extension in your receiver is without any flaws, you could still have small gaps in the fit. You could double up and use some 620 to take care of those voids but you'd need to make sure that whatever epoxy you use is compatible w/the 620.

As always, your best bet is to start with the best fit that you can from the beginning. BCM offers forged upper receivers with slightly undersized barrel extensions which should give you a pretty good fit from the start (I still use 620 on these). Billet uppers are always an option too and usually offer a tighter fit (but not always).

[bj139]

Won't steel shim stock rust? I've heard of people using aluminum.
Most people here just use blue locktite to fill the gap.

[A5BLASTER]

Won't steel shim stock rust? I've heard of people using aluminum.
Most people here just use blue locktite to fill the gap.

Haven't had a problem with mine rusting at all.

[Huckleberry75]

I have lapped the face. Just wasn't sure what to use as a release agent, so it's not permanent.

[bj139]

I have lapped the face. Just wasn't sure what to use as a release agent, so it's not permanent.

Blue Loctite is not permanent. If you are worried you could rub a little paste wax inside the receiver and then wipe it off well.

[Klem]

Someone's got to say it...Not everyone glues (beds) their barrels to the extension. Gluing an AR is a different situation to bedding a bolt gun. It would be equivalent to gluing the join between the barrel, recoil lug and receiver on a bolt gun. Bedding refers to an intimate surface area contact between the receiver and stock. There is no equivalent to this in an AR. It is false logic to transfer the sensible reasons we bed a boit gun to the practise of gluing a barrel to the receiver in an AR.

I tried gluing the barrel to receiver a while back using Loktite 641 and it did not improve scores. The fit was already tight however with the glue being forced out as the two parts were tapped together. My thoughts are it depends on how loose the join is and if you have a tight fit then replacing grease with glue is no guarantee of tighter groups. I can see the benefit however if the fit is loose.

My advice on accurising an AR is to buy the best barrel you can afford. Even skimp on other parts if you're on a budget. Then scope, then trigger. Then consider the barrel as a consumable item that you replace, perhaps every year depending on the round-count. Gluing barrels just makes that job more difficult and tedious as you go to some effort to release the old barrel and clean-up the mouth for the next barrel.

That's my experience with gluing, and I'm sticking with it (pardon the pun).

Some shooters will glue their barrels religiously and this gives them peace of mind that they have done something more than MILSPEC that hopefully improves accuracy. I can see in this context the cost of the effort might be worth it. At the end of the day you've got to be confident with what you've got.

[grayfox]

The other un-mentioned elephant in the room is to buy better uppers, ones that have tight or nearly (NEARLY) impossible fits, then heat them for a secure fit.
If there's a brand that gives loosey-goosey fits, get rid of it and don't buy that brand again (Klem has already discussed the good barrel, I don't bring that up again). Think of that upper as the extension to your barrel.
For me that means BCM and Aero, both of those have yielded tight fits from the git-go.
My $0.02.

[imaguy3]

Someone's got to say it...Not everyone glues (beds) their barrels to the extension. Gluing an AR is a different situation to bedding a bolt gun. It would be equivalent to gluing the join between the barrel, recoil lug and receiver on a bolt gun. Bedding refers to an intimate surface area contact between the receiver and stock. There is no equivalent to this in an AR. It is false logic to transfer the sensible reasons we bed a boit gun to the practise of gluing a barrel to the receiver in an AR.

I tried gluing the barrel to receiver a while back using Loktite 641 and it did not improve scores. The fit was already tight however with the glue being forced out as the two parts were tapped together. My thoughts are it depends on how loose the join is and if you have a tight fit then replacing grease with glue is no guarantee of tighter groups. I can see the benefit however if the fit is loose.

My advice on accurising an AR is to buy the best barrel you can afford. Even skimp on other parts if you're on a budget. Then scope, then trigger. Then consider the barrel as a consumable item that you replace, perhaps every year depending on the round-count. Gluing barrels just makes that job more difficult and tedious as you go to some effort to release the old barrel and clean-up the mouth for the next barrel.

That's my experience with gluing, and I'm sticking with it (pardon the pun).

Some shooters will glue their barrels religiously and this gives them peace of mind that they have done something more than MILSPEC that hopefully improves accuracy. I can see in this context the cost of the effort might be worth it. At the end of the day you've got to be confident with what you've got.

This... It's stupid and I hate it.. I haven't bedded any of the AR's I've built for myself or buddies, close to 12 now. All used a well made upper and a good barrel, ALL of them shoot under or damn near MOA after finding a load it likes...

[NugginFutz]

I've gone with forged uppers, billet uppers and heavy extruded uppers. I can only say that ALL can shoot well, so long as the fit is good, and there is no opportunity for movement of any kind between the upper, barrel extension and barrel (yes, I have read where a builder or two has had their barrel spin loose from the extension while torquing a muzzle device).

I have three AR's which shoot very nice, tight little groups. 2 BHW's and a Larue. (3 BHW's, if you count a 5.56). Not one of them has a "hammer it in" tight fit, let alone needed heating of any components. Barrel lengths range from 18" to 22", and profiles vary from Bull (.986") to Standard (.750").

The two things that are common to all my accuracy guns are - (just sip your beer for a moment, Klem) - Lapped upper receiver faces and Blue Loc-tite. In the interest of full disclosure, though, one of the BHW's was already shooting very nice groups prior to my replacing the hand guard and reassembling with Loc-tite.

I believe that getting things flat, tight and true are the basic fundamentals, here. Everything else is pretty much personal preference.

[centerfire]

I wonder if the "Indian Head" that centerfire referred to above is similar to Loctite Green 620?

They are not the same. Indian Head looks like molasses.

[centerfire]

The other un-mentioned elephant in the room is to buy better uppers, ones that have tight or nearly (NEARLY) impossible fits, then heat them for a secure fit.
If there's a brand that gives loosey-goosey fits, get rid of it and don't buy that brand again (Klem has already discussed the good barrel, I don't bring that up again). Think of that upper as the extension to your barrel.
For me that means BCM and Aero, both of those have yielded tight fits from the git-go.
My $0.02.

I have a high quality machined billet upper that fits loose with a very high quality barrel, sometimes parts aren't at the same end of the tolerance. The rifle shoots very well despite the fit up but it is glued in with Indian Head.

[Swampfox]