Ar barrel nut torque settings new barrel

[Ford SD]

Not a gun smith but looking for help
Have done some small stuff on my own rifles

Building Ar 300 blackout from parts
(new barrel)
Told/ read read Ar barrel nut torque settings are 30 ft LB min
Brownells start 30 -35 max 40 ft LB

other places 80max read also 100 max but its the internet and I wont try 100
for it to turn that far the threads have to stretch
Upper is aluminum / barrel nut aluminum
first time 30 ftlb close but rubbed (too far past) app 2-3 deg
next hole is so far off that it in another state
backed off
26 too far away ( past)
backed off
24 too far away ( past)
20 is too far away ( past)
15ftlb is not far enough need app 17 LB to align gas tube to upper/ barrel nut

even took it apart and cleaned off most of the antisize
tried 38 ftlb and not even close to the next hole
too chicken to try to go to 100 ft LB
I own 5 torque wrenches and know how much 80 LB is == broken parts on aluminum /steel
(1/4inch and up)

What can I do

I can cut a thin shim for between barrel extension and barrel nut and try again

I should be able to cut a 0.001 or 2 shim thick (ring) and try again

Thanks for ideas and the help

[nhrifle]

Ok, I've built a few of these, including a 300 Blackout like you are doing. It's not that hard, but torquing the barrel made me nervous the first time. I have never used a torque wrench on mine, only the barrel nut wrench. Just lube the threads on the upper receiver with a good moly-based grease (I can't recommend never sieze like you are using but have never tried it), I used synthetic brake caliper grease. Degrease the barrel extension and the inside of the receiver. Insert the barrel into the receiver and hand tighten the barrel nut, giving the barrel a little up-down and side-to-side wiggle at the same time. Use the barrel nut wrench to snug the nut firmly. Loosen the nut, then retighten it. Repeat a few times. This helps to seat the barrel squarely and "mash down" any irregularities. Give the nut a good tightening with the wrench. The gas tube clearance probably won't be lined up.

Now, do not loosen the nut to go back to a closer tooth as that is asking for a loose barrel after firing a few shots. Install an alignment tool in the upper through the gas tube hole. I use a drill bit, don't remember exact size but it's around 1/8" or #16. Turn the barrel nut a tiny bit at a time until the drill bit aligns perfectly between a cutout on the nut and the hole in the upper.

You may have to go quite a bit to get it to line up. My second build was so far off after intial tightening that I had to turn it almost a complete tooth. As long as you are using a quality grease on the threads and go slowly, you won't have a problem.

Feel free to PM me if you have any concerns or if I wasn't too clear. Let me know how it turns out and how it shoots. I love my Blackout! Never knew an AR could be that much fun to shoot!

[Ford SD]

Did I @@#$ UP

Well I cut a shim and installed it in front of the barrel nut shoulder
.005 thick alum
Barrel nut finger tight (no Wrench)
put the Torque wrench on it and started at 25lb checked gas tube
Plus 5 checked
plus 2 checked
plus 1 checked
plus 1 checked very close
plus 1 lb checked and perfect
= 35 ftlb total

finger tight plus 1 hole =35 ftlb

doing it this way Am I going to have a problem later on ?????? because of the shim

Thanks

First Ar build btw

[nhrifle]

I have never seen one built or fired with a shim so I would take it back apart. The final torque in not as important as it being tight. Too loose is too loose, but tight is good. I have also never heard of anyone removing the threads from a receiver by overtighttening the nut. Like I said, I had to turn one almost a complete tooth, and I uttered a few very nasty words while I was tightening it! The neighbors were not impressed.

[nhrifle]

No, I don't think you ruined anything.

[blikseme300]

The shim should not cause any problems but accuracy might be affected. What I do when doing builds is to lap the face of the receiver. This ensures that it is perfectly square and the length can be adjusted. See it here: http://www.midwayusa.com/product/810457?cm_vc=S014

[tomme boy]

I like to tighten it down an loosen it up at least 5 times. Then torque it down to at least 35 ft lbs. Then tighten it to the next alignment slot on the barrel nut. If I remember right the torque setting is 35-75 ft lbs. Never loosen it to align the nut.

[nicholst55]

Most anti-sieze products are a graphite grease with either nickel or silver added. Graphite will cause serious corrosion when it comes into contact with aluminum. The anodizing might prevent this, but ask yourself if you want to take the chance. Most auto parts stores carry moly grease for just a few bucks, so why risk it?

I've been wrenching on M16s and AR-15s since 1973. Never used a shim to obtain proper barrel nut alignment, but doubtless could have a few times if I'd had them. I know of only one professional AR-15 smith who uses (and sells) them. Lapping the upper is a better idea IMHO. IMHO, if you have to apply more than about 40-45 Ft-Lbs of torque, you're very likely going to distort the upper receiver. The billet uppers are probably safer than standard forged uppers (especially flattop uppers), but I'd be nervous with any upper in that situation.