Home Forums Hunting & Shooting AR and Tactical Rifles Who beds there barrel Extension into the upper. On ar builds.

I have a aero upper that was just not as tight as I would like. (Not loose but).
So I shot some Brownells quick bed bedding compound on the extension and gave it a good one spin to the tit. Wiped it up. Put the nut back on and then torqued it to 70 foot pounds wiped all the extra off inside and out at each step hoping it tightens groups up. If not I'm going to toss it. Anyone else doing this to get the best fit possible.

Should have taken pictures but was in a hurry if it works I have another that I will photo as I do.

Yes, bedding with Loctite is common, although I'm sure bedding compound works well too. It's a good practice to improve accuracy.

Some like to use shims to tighten the fit. Personally I use green Loctite 680. You can put a release agent on one part if you don't want to glue the barrel and upper together. Otherwise, will need heat to get them apart without damage.

Another option, not for yours but for future reference, is using an upper that is an interference fit on the barrel extension, so you have to heat the upper to install the barrel. BCM sells their uppers this way, not sure who else. The BCM upper I just got in the mail is ~.004" smaller ID than the barrel extension OD.

I use loctite but I keep the torque down to 40' pounds and square.

The thing about bedding is filling the voids while keeping things true and stress free. Too much torque can cause stress all by itself.

I had shims to get 50"# but once the bedding compound was involved it took 70"# to line the gas tube up and I was a bit worried taking it apart to remove a shim would make me end up shy in the other direction.

I also did some tweaking on the gas tube and made sure it was not touching the gas block when closed. Kinda a tedious process. I will post if it helps or not once everything has dried for 24 hours.

The bmc upper sounds like the way to go if a guy buys a high quality barrel and bolt. A heat fit upper makes lots is sense.

After researching the idea of bedding, I'm going to wait until I get home tomorrow and measure my Aero AR10 upper, which I've had for a while, and Faxon .308 barrel, which arrived last Monday.

First thing I'll do is check the squareness if the upper. If it isn't right it will get trued.

If there is a significant difference in the diameters of the upper and barrel extension I'll have to make a decision as to what to do about it, if anything. Loctite 620 and 680 are more permanent than I would like. Maybe brass shims?

If there is any play, I put red loctite on the barrel extension.

Had a chance to shoot my 5.56 today after the 24 hour dry period. Groups with 35 gr , 55 gr , and 77 gr all got better by about .3" the 77 went to 1/2 from 3/4 " the 55grn are at .5 for five now easily and the finicky 35 went at 1 1/2" for twenty. The 55 grs will be the gopher exterminator for the summer. The Brownells quick cure glass did a great job.