AR-15 with barrel nut alignment issue

[MEAT4272]

Hello Folks,

I'm coming up on finishing my first AR-15 build and I have hit a snag... I'm having alignment trouble with the J.D. Machine Upper & Larue barrel nut. I'm using a moly based grease on the threads, I have torqued, taken lose and torqued again the barrel nut ranging from 30 to 80 foot pounds with no new results.

My question, is it safe to go above 80 foot pounds?

Also, the barrel nut comes into alignment between 20 and 25 foot pounds with using a 5-pin PRI barrel nut wrench and 1/2" Craftsman click type Torque wrench.

For this build I'm using the following parts combination.

Lower Reciver: JD Machine.
Upper Reciver: JD Machine.
Lower Parts kit: Colt.
Upper Parts Kit: Colt.
16" Barrel, Mid-Length Gas System: White Oak Armament.
Phantom Muzzle Brake: YHM.
N/M Bolt Carrier Group: Young Mfg.
Raptor Charging Handle: Rainier Arms.
Enhanced Takedown & Pivot Pin Set: Battle Arms Developement.
CASS-SA Ambi. Selector Switch: Battle Arms Developement.
Bolt Catch: Seekins Precision.
Billet Mag Release: Seekins Precision.
Trigger Assembly, SSA: Geissele.
Tele-Stock Assembly, Mil-Spec. & H2 Buffer: Cavalry Manufacturing.
Buffer Spring, Blue Spring: Tactical Springs LLC.
A2 Pistol Grip: Cavalry Manufacturing.
9" Handguard LT15-9, Free-Float: LaRue Tactical.
Post-Ban Front Sight Assembly .052 Post, Set Screw Base: White Oak Armament.
Nitrocarburized Gas Tube, Mid-Length: WMD Guns.
Carry Handle Assembly, Rear Sight 6/3: Colt.

I will post some photos once I get this alignment issue solved and I'm able to complete the build.

Thank you Folks for any and all help you can offer.

 

[davebl]

How far off are you?

 

[MEAT4272]

I'm about 3/4 to the next hole.

 

[MEAT4272]

I forgot to mention a few things...

The barrel nut wrench is from PRI, it's the 5-pin tool and it has a handle.

The centerline is 2" from the barrel to the torque wrench drive.

I'm using the torque wrench with the length of the barrel nut wrench handle.

Thanks again for the help!

 

[JBomb]

Do you have directions from PRI for their tool?

The farther you move the torque wrench from the centerline the more foot lbs of torque you apply to the nut. Are you taking this into account?

Kind regards,

Jared

 

[MEAT4272]

No directions came with the wrench. I did know about the increase in torque, but I have not yet found any information on how much the increase is based on the 2" centerline.

Thank you !

 

[303_enfield]

Well, you can true the front of the receiver using this:
AR-15/M16 UPPER RECEIVER LAPPING TOOL | Brownells

Otherwise go with the 25 ft/lbs as the USGI -10 standard is 30-80 ft/lbs.

Also, wipe the grease off. You just need a little bit. Then torque three times, taken it on and off. Then try to see if it lines up. If not do it again.

The above tool will fix it.

 

[wareagle700]

I lap the front of my receivers using the tool above to get perfect barrel nut alignment and 50-75 ft/lbs of torque. I would not try going over 80.

If you have a hard, very flat surface and some 600-800 grit sandpaper you can remove a very slight amount of the receiver face (not even enough to remove the finish) to get your barrel nut aligned. Set it up and twist/turn the receiver on the sand paper, no front to back strokes.

Obviously the lapping tool above is the right way to do it though.

 

[JBomb]

Depends on the length of your torque wrench but assuming you have a 12" torque wrench and you add 2". Your essentially adding 16% more torque to the nut....so with a 25 ft. lb. setting, your only off 3-4 lbs.

 

[wilb]

Try using other barrel nuts. I've had the same thing happen, and found another nut that went together a bit easier. I've also used more than recommended torque, about 94 ft,-lbs, with no obvious problem. A lot of folks are over torquing because they are not accounting for the arm from the torque wrench to the center line in the barrel nut wrench.

Torque wrenches need to be checked occasionally, you can use a simple calibration device on most Snap-On trucks.

 

[werew]

I had this issue with a couple builds and I don't exceed 65 ft/lbs of torque (to me... 55-60 ft/lb is ideal torque). Here's what I do... I start with a very clean barrel nut and receiver threads(and mating surfaces). After cleaning always re-apply a very light amount of anti-seize or grease onto the receiver's threads, never torque the barrel nut down on dry threads. Then torque barrel nut down to 40ft, observe & back off, 45ft, observe & back off, then 50ft. Observe in between each torque how much/if it's moving. Then give it a good cleaning, lube and restart process at 50ft, 55ft, 60ft. I usually hit the jackpot (timed @ 60'ish ft/lbs) after 2-3 clean/torque/loosen processes. I use tri-flo grease, I think tw-25B, anti-seize or lithium grease would work well also.
What we're dealing with I think is moreso using new parts.... stacked tolerances.
1. new surfaces mate up/seat better
2. sharp edges getting knocked off
3. micro-rough surfaces from anodizing/machining/finish getting smoothed out. Use an eye loop, you can see the surfaces get smooth.
In a sense it's micro-polishing/lapping, each time you clean you're removing grease with micro-shavings-grit in it and allowing your barrel nut to be turned a little more.

I wouldn't recommend using sandpaper on the receiver face, unless you have a lot of patience to develop a "feel" to how much material you're taking off, it'd be easy to take off too much and be right back where you started or you could knock receiver face out of square. If you want to try sandpaper(i've lapped muzzlebrakes this way to time them), use 800grit and on a glass surface with some very light oil and exert no downward force on receiver, let it's weight do the work and focus on making very smooth (dont let receiver hop or tilt) figure 8's with the part, dont twist or rotate receiver on the sandpaper. Clean, lube and check the fit often. The tool from brownell's seems like a good idea, but unnecessary if one has some time and patience.

A little about me, I used to build CNC machines for a company called Mazak/Yamazaki and worked in a clean room building the spindles. The bearings inside the spindles required spacers to be uniquely surface ground and hand-lapped to be within +/- 2 microns of tolerance to achieve proper "press" on the main bearings. Too little press and the spindle shaft would have endplay, too much press and... catastrophic failure on test stand during it's 24 hour break-in. LOL so im sort of a... perfectionist when I work on these sort of things.
Good Luck!

 

[KTDLS7]

Depends on the length of your torque wrench but assuming you have a 12" torque wrench and you add 2". Your essentially adding 16% more torque to the nut....so with a 25 ft. lb. setting, your only off 3-4 lbs.

Your correction calculation is correct 16% (actually 16.66666%), which works out to 5-5.8 lb/ft using 30-35 lb/ft constant. But, it makes no difference if you have a 6", 13", 27" or 72" torque wrench. The longer torque arm will require less effort to attain the given torque. A lb/ft torque wrench is calibrated in lb/ft, regardless of length. The only correction required is the distance from centerline to center of drive square.

OP, if you can align the gas tube on 25 lb/ft, you are on in spec on the lower side.

 

[KUSA]

Just keep working it back and forth (tighten and loosen without a torque wrench) until it reaches the next alignment hole. I don't use a torque wrench on it but I have been turning wrenches for 27 years so I have a feel for things.