Not an adhesive.Working on my first AR build and scrutinizing over the details. What’s the consensus around here on using some sort of compound/adhesive when seating the barrel? What do you use?
Last one I did that way, I had no wife to help, so a 2x4 was involved.I used stainless shim stock and a thermal seating on a 6.5 Grendel build I did back in 2020. I premeasured the clearance between the barrel extension and the upper and then used shim stock that was slightly larger. The thermal fit involved heating the barrel channel of the upper with an induction coil and chilling the barrel in the deep freeze for a couple hours. I wrapped the shim stock that I had precut around the barrel extension with the seam at the top by the locating pin and held it in place with a rubber band while the barrel was cooling. Once you get to the seating part it is a a very time sensitive process. I had my wife heat the receiver while I pulled the barrel straight from the freezer, removed the rubber band and quickly slid the barrel into the receiver as my wife moved the heating coil. The barrel was seated solidly and will not come out without using a lot of heat.
Yes and I believe the lapping also may help remove imperfections in the anodizing process. I've used a piece of glass with some wet sandpaper. Also, apply a bit of anti-seize to the threads. Pick up a couple extra 'ketchup' packs of anti-seize the next time your at your local auto parts store. Its handy to have. YMMV.I remember reading about gaining some accuracy by lapping the front of the receiver face so the barrel extension shoulder has a nice true surface to mate to.
Havent done it myself yet but plan to if i do another accuracy build.
Never used anything on the threads and am yet to have a problem getting them off. Although I've never gotten my rifles super hot either. Mileage my vary.
Entirely unnecessary, unless used in the case of fixed-position breech bolts like dedicated .22 uppers. Maybe.I remember reading about gaining some accuracy by lapping the front of the receiver face so the barrel extension shoulder has a nice true surface to mate to.
Havent done it myself yet but plan to if i do another accuracy build.
Never used anything on the threads and am yet to have a problem getting them off. Although I've never gotten my rifles super hot either. Mileage my vary.
I used stainless shim stock and a thermal seating on a 6.5 Grendel build I did back in 2020. I premeasured the clearance between the barrel extension and the upper and then used shim stock that was slightly larger. The thermal fit involved heating the barrel channel of the upper with an induction coil and chilling the barrel in the deep freeze for a couple hours. I wrapped the shim stock that I had precut around the barrel extension with the seam at the top by the locating pin and held it in place with a rubber band while the barrel was cooling. Once you get to the seating part it is a a very time sensitive process. I had my wife heat the receiver while I pulled the barrel straight from the freezer, removed the rubber band and quickly slid the barrel into the receiver as my wife moved the heating coil. The barrel was seated solidly and will not come out without using a lot of heat.
Good post, except you're not really current on high-accuracy AR work. The following will focus on that, as I don't presume to know much about heavy full-auto usage.WHAT THE ACTUAL HELL?
This is not an area of mystery or debate or need for varied and innovative technique or experimentation. This is long established procedure where I am going reference for the second time in recent days military experience in the initial production and servicing of, no exaggeration, millions of rifles.
People are actually talking about creating whole new potential problems if anything, for a procedure that is straight forward and very well documented for decades. There are a lot of things that are complex, or uncertain, or debatable; this is not one of them. There are a lot of things that are subject to careful testing to determine and validate what works best. Already done for us long ago.
Some folks have correctly noted the bolt locks into the barrel extension so that the connection between the barrel and the upper receiver only needs to the keep the barrel attached and the receiver channel where the bolt carrier reciprocates generally in a straight line with the barrel axis. There is no need to have the barrel extension with an extremely tight fit into the upper receiver, or have adhesives or shims present here which are only going to do some of three things if anything, none of which are helpful: 1) You are going to impede the free movement of the barrel extension seating back into the receiver so that it jacks up the barrel nut torque which is your indicator for that operation on initial mounting, or future remounting with now setup adhesive present in that space. 2) You are screwing up clearances that in part accommodate the differing thermal expansion rates of two very different alloys in conditions from the Arctic to the maximum recommended rate of full auto fire. 3) You may be stressing a relative thin circumference of much weaker aluminum surrounding the steel barrel extension.
Finally the torque ratings for AR barrel mounting assumes lubricated threads. In fact, I have seen through first hand experience where torquing dry threads resulted in the barrel nut loosened with thermal cycling where the gas tube passing through the barrel nut was the only thing preventing the rifle from disassembling itself.
Quoting here from the closest reference I could reach on the shelf, October 1984 USMC M16A2 technical manual. Apply molybdenum disulfide grease to upper receiver barrel nut threads. Assuming your barrel wrench has a similar offset from the barrel axis to the square hole for a standard torque wrench as the USGI barrel wrench, torque to 31-35 ft-lb. Loosen and repeat. Loosen and repeat. Third torquing is the charm, hopefully plus or slightly minus enough rotation to line up the barrel nut to allow proper alignment of gas tube.
You are set now unless you ever need to remove that barrel and it will be simple to do without damaging anything once the gas tube is removed. The only grief in a higher mileage upper is sometimes driving the damn gas tube pin out of the front sight base, if so equipped.
The instructions for using BCM’s barrel nut, required with a BCM handguard, state that oil MAY ease installation, and to never use grease.
These barrel nuts do not have to be timed to let the gas tube through, I actually had no idea the original design did. That would kind of suck. Just shows we don’t know what we don’t know.
3. Apply white lithium grease or moly paste to the threaded area of the inside of the KMR barrel nut (Item No. 1)
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9. Note: Application of oil to the exterior of the barrel nut may ease installation. NEVER use grease of any type on the exterior of the barrel nut.