AR15 Handguard - How is it kept tight?

[11Charlie]

because they ship so much stuff they get commercial prices and free pick up at there location

 

[titsonritz]

I'd like to install one of those fancy machined handguards with the Picatinny rail along the top to one of my phantom AR-type rifles. The original barrel nut is toothed, and the gas tube through the teeth is what keeps the nut tight. These new handguards have a barrel nut that doesn't look to have any teeth to prevent loosening of the nut. What keeps the nut tight? If it's just friction, that doesn't seem to me like it's going to work for too awful long...

The teeth on the standard barrel have nothing to do with "keeping the nut tight". The barrel is held in place via proper torque, which for a standard GI barrel nut is 30-80 ft.lbs. the teeth are used to engage armorers tool or barrel nut wrench and must be properly timed to allow the gas tube to pass. Most handguards these day have a proprietary barrel nut without teeth like the GI nut and do not require timing.

 

[titsonritz]

I'd not want to put loc-tite on those threads. I put a drop too many on the buffer tube threads of another one of my phantom AR-type rifles a number of months ago. I then wanted to install a QD endplate a couple of weeks ago. The castle nut was so tightly adhered to the endplate that the little alignment nub on the OEM endplate rotated with the nut and buggered the threads. A quick hit on the ebay website and about a week of waiting had me a new tube and castle nut. I now use one sparing drop of loc-tite to secure the castle nut.

I have seen these types of handguards offered with two wavy washers. I'd have to assume the wavy washers are what maintain friction once the barrel nut has been tightened. I'm a mechanically-minded person. I prefer nuts and bolts over "modern composite adhesives." One of Boeing's new wide-body jets is glued together. You won't see my assets on that jet...

Loc-tite should not be used the receiver extension castle nut. Per TM 9-1005-319-23&P molybdenum disulfide grease should be applied to the threads, the castle nut should be torqued 38-42 ft.lbs. and the receiver end plate should be staked in two places.

That said, there is nothing wrong with using Loc-tite on handguard screws. As a general rule of thumb I use blue Loc-tite for anything with threads except gas blocks in which case red should be used. For small screws such as scope rings where torque is measured in in.lbs instead of ft.lbs, I'll use purple (which is what Geissele recommends).

 

[nvshooter]

Just ordered a barrel nut wrench for my new handguard. Made a mistake; ordered one with a 1-3/16-inch opening. Need one with a 1-1/4-inch opening. Saw the second one just a few minutes after completing the order for the smaller wrench. Sent a message to them about the error; hoping they can pull the order before it goes onto the truck. Mentium ships orders via USPS, so the truck will most likely not arrive until 1600 CST. Order was placed around 1400 CST, so there is a chance the seller can terminate the order before it is shipped.

Good news! Mentium was able to cancel and refund the order for the incorrect wrench before the order went out the door. That is customer service! They have saved me a ton of time and effort. I have already emailed back to them that I am ecstatic with how well they handled the problem. Not only that, I have ordered the correct wrench as of tonight. We're only talking about sixteen bucks or so, but it's the principle. I do not need the 1-3/16" wrench, and Mentium got their act together and saved me the trouble of sending it back and all that jazz associated with merchandise returns. I'm a happy camper. I can now put the fancy handguard onto my phantom rifle...

 

[nvshooter]

Loc-tite should not be used the receiver extension castle nut. Per TM 9-1005-319-23&P molybdenum disulfide grease should be applied to the threads, the castle nut should be torqued 38-42 ft.-lbs. and the receiver end plate should be staked in two places.

That may be how Uncle does it (or wants it), but I use a drop of blue Loc-Tite and tighten the nut to where it's snug. I'm guessing I have maybe ten to twelve foot-pounds of torque on the nut. It's "tight," but not so much that I won't be able to get it off at a later date. Years ago, I used a drop or two of red Loc-Tite on the castle nut. I had no idea the stuff was so strong. I had to use a pipe wrench to loosen the nut, which destroyed it. I do not remember if the wrench was 18" or 24" long. That was the last time I ever used red Loc-Tite on an AR-type rifle; I will never use any of it again on any firearm...

 

[Joe Link]

That may be how Uncle does it (or wants it), but I use a drop of blue Loc-Tite and tighten the nut to where it's snug. I'm guessing I have maybe ten to twelve foot-pounds of torque on the nut. It's "tight," but not so much that I won't be able to get it off at a later date. Years ago, I used a drop or two of red Loc-Tite on the castle nut. I had no idea the stuff was so strong. I had to use a pipe wrench to loosen the nut, which destroyed it. I do not remember if the wrench was 18" or 24" long. That was the last time I ever used red Loc-Tite on an AR-type rifle; I will never use any of it again on any firearm...

Yeah, that red loctite is strong stuff!

 

[nvshooter]

Yeah, that red loctite is strong stuff!

It's billed as being "permanent," but it melts at 325 degrees. Problem is, if what you want to take apart cannot handle 325 degrees without being destroyed, it is permanent...

 

[titsonritz]

That may be how Uncle does it (or wants it), but I use a drop of blue Loc-Tite and tighten the nut to where it's snug. I'm guessing I have maybe ten to twelve foot-pounds of torque on the nut. It's "tight," but not so much that I won't be able to get it off at a later date. Years ago, I used a drop or two of red Loc-Tite on the castle nut. I had no idea the stuff was so strong. I had to use a pipe wrench to loosen the nut, which destroyed it. I do not remember if the wrench was 18" or 24" long. That was the last time I ever used red Loc-Tite on an AR-type rifle; I will never use any of it again on any firearm...

That is why anti-seize grease it specified on both the castle nut and barrel nut, it assumed the weapon will at some point be rebuilt.

It's billed as being "permanent," but it melts at 325 degrees. Problem is, if what you want to take apart cannot handle 325 degrees without being destroyed, it is permanent...

Which is why it is only used on gas blocks.

 

[nvshooter]

Which is why it (red loc-tite) is only used on gas blocks.

I've seen videos of gas tubes getting orange, but I doubt a gas block gets to 325 degrees. It might, but I'm too smart to touch it and find out. I like clamp-on gas blocks; they can be gotten really tight, and do not require a hydraulic press to drive them off.

 

[nvshooter]

Received 1-1/4" barrel wrench from Mentium USA. It is overly wide by 0.052 inches, as measured against the barrel nut. Will have to glue a feeler gauge (or a strip of aluminum from a beer can) to one finger of it to reduce the chances of the wrench slipping and rounding-over the corners of the barrel nut. I now have the tools; all I need is the time and a tsunami of ambition to get at it and get it done...

 

[targetshooter]

shipper gets volume discounts

 

[Stomper]

I would just like to point out that the gas tube does NOT keep the MILSPEC barrel nut tight, that's what the torque force against the shoulder of the barrel extension is for. If torqued properly the barrel nut shouldn't be in any significant contact with the gas tube under any operating condition.

Hope that helps!

 

[nvshooter]

. . . the gas tube does NOT keep the MIL-SPEC barrel nut tight...

No; I will grant you that point. But the gas tube going through the nut's teeth will certainly not allow the barrel nut to get loose. It's just the design of the direct-impingement system that has the tube going through the teeth exactly where it does. Had the design been finalized a few millimeters this way or that, the tube might well have not gone through the teeth, and this discussion would have possibly never taken place.