Questions about AR-15 Barrel Nut & Hand Guard Installation

[pert near]

OK. I hope THR subscribes to the notion that no questions are too stupid & I won’t be stoned to death!

I’ve built (assembled seems more appropriate) several AR-15 lowers with the help of books & YouTube’s. They turned out great, fun & informative. Now I have decided to build my first upper & I have been collecting my needed parts via recent sales & bargains. I have a custom ARP barrel (SIX5 caliber) & an Anderson upper receiver. I intend to square-up the receiver front for the installation. This will mainly be an informal target punching rifle. As in the past, I have been reading articles & watching YouTubes for my armorer’s training.

I bought this handguard with special barrel nut, screws & plate. The plate has a small tab on it(?) This seems to be a first-rate rail. It is supposedly a manufacturer’s over-run so it bears no brand name. The barrel nut is round & smooth with two flats across for tightening. It also has 4 each ½” holes drilled around at 90 deg that could align with the guard. No instructions available.


Here are my questions:

• Is this barrel nut sufficient for attaching the barrel to the receiver without additional nuts, washers, springs, shims, etc.? Am I missing something here?
• The smooth design using this barrel nut alone means no “clocking” is necessary to align the gas tube with the bolt gas key. What I have been reading states that barrel nut torque is acceptable between 35 & 85 ft/lb. In this situation, what torque is ideal?
• I have a ½” drive torque wrench but I don’t have a 1-1/8” crowsfoot wrench head. It also looks like the nut design may not allow the crowsfoot & drive head to be close enough to fit. So I’d have to add an extension to offset this to get it to work. But I do have a large crescent wrench that fits just fine. Is it possible to tighten with the crescent & somehow estimate the proper torque, especially if it doesn't seem to be so critical across a 50lb range?

I hope all of this makes some sense.

TIA for any help or suggestions!

 

[Blue68f100]

The nut is all you need, no extras required. As far as torquing, there is such a large span it's not that critical. Just load it 3 times to get it to settle down. If your going for the upper end it's best to use a reaction rod to torque the barrel so you don't load the upper. http://www.brownells.com/gunsmith-t...-reaction-rod-prod55168.aspx?avs|Make_3=AR-15

 

[BBBBill]

^^^^ What he said. However, since you seem to enjoy this and may continue to build more, perhaps spending the money for some "proper smiffin'" tooling will serve you well. Getting by is just that.

Back to what he said. Excess torque has killed a lot of upper receivers. They are not strong in that plane. The reaction rod is by far the best protection for the receiver and I'm guessing provides the most accurate torque results as it will eliminate any flex issues with the upper. At the very least use a clamshell type vise block for the upper.

This will mainly be an informal target punching rifle.

Depending on just how accurate you want this to be, you might want to scrounge the series of articles by Joe Carlos in American Gunsmith magazine. He's formerly of the USAR rifle team and built a lot of match winning guns. A real wealth of info in those articles on some things that you would most likely never think of.

 

[pert near]

Thanks for the good info. I have collected most of the tools that I need including clam-shell receiver blocks. I definitely can see the value of the reaction rod.

Since barrel nut torquing is not a problem with my set-up what would be the most ideal setting? Set at minimum, say 40 ft/lbs or split the range difference & set at 60 ft/lbs?

 

[BBBBill]

Were it mine I would go between 40 and 50 pounds. Aluminum will stretch. The more you stretch, the shorter the life span. My quasi-scientific belief is that will give you a better opportunity to reuse/re-barrel the receiver more than once or twice. You can always go a bit tighter if you sense the need.

 

[Centurian22]

Another (less expensive) option to the rod is the Magpul Bev Block at around half the price. This is what I chose for my first build and I love it so far. Especially once secured by the BCG on the back end it is a solid lock up. Served me perfectly for installation of my barrel with the ALG EMR and included barrel nut. I agree with the above on 40-50 as a goal. If using any type of extention (including any "normal" barrel nut wrench) keep in mind that it will alter your torque specs. The proper orientation of a barrel wrench to the torque wrench (to my limited understanding) is actually 90 degrees (perpendicular) to the handle of the torque wrench as the length from handle to head is a factor in the torque spec. Good luck with the build!