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  #1  
Old 12-16-2012, 12:43 PM
jvh22a jvh22a is offline
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Default ar15 barrel nut tightness

this is my first ar15 assembly and i got the nut on and did the tighten/loosen about 10 times aready. the fingers on the nut will always end right at the openning for the gas tube. at 50lbft the finger will be in the way as i tighten to max 80 it will almost clear. just a bit more.

in your opinion should i just tighten it down just a bit more? cause if i loosen the nut it i would be in the 30lbft range. and that is just a bit tighter then hand tight.

compensator is already welded on and gas block in place so dont want to remove those.





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  #2  
Old 12-16-2012, 1:12 PM
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That's what I did. works fine.
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Old 12-16-2012, 1:32 PM
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You could remove the offending tooth.
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Old 12-16-2012, 1:37 PM
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I recommend putting a liberal amount of oil on the threads and do the tighten / loosen thing more until you get it to the tighter spot. I would not cut off the tooth.
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Old 12-16-2012, 2:34 PM
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My USMC manual says tighten to 35 ft lbs, check alignment and tighten to next hole if needed for proper clearance of gas tube.
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Old 12-16-2012, 2:37 PM
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you can file a bit off the front of the upper just enough to take the finish off it also helps with the retaining pin wear on the buffer sometimes

also use anti sieze paste on the threads
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Old 12-16-2012, 3:11 PM
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Whoa, you're torquing this nut 50 to 80 foot pounds? That's WAY too much!

Top end torque should never be above 40 foot pounds, and the range is more like 23-40 ft-lbs that you should be torqing it to!

Really, I've seen people using their AR-15s with the barrel nut torqued hand tight. If you're going up to 80 foot pounds, you're destroying the threads on your ALUMINUM upper receiver!
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Old 12-16-2012, 5:25 PM
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For the openning to line up the torque is only 10lbft, little less then hand tight. 40lbft the finger is right in front of the openning. So to get it to the next openning the torq will be near/pass 100lbft.

For those that filed fit, does the gas tube help with lining up the bcg?
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Old 12-16-2012, 5:36 PM
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Quote:
Originally Posted by jvh22a View Post
this is my first ar15 assembly and i got the nut on and did the tighten/loosen about 10 times aready. the fingers on the nut will always end right at the openning for the gas tube. at 50lbft the finger will be in the way as i tighten to max 80 it will almost clear. just a bit more.

in your opinion should i just tighten it down just a bit more? cause if i loosen the nut it i would be in the 30lbft range. and that is just a bit tighter then hand tight.

compensator is already welded on and gas block in place so dont want to remove those.





I would tighten a hair more .That would be ok.Did you forget to use never-sieze on the threads.?The stuff you put on brake pad calipers bolts.
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Old 12-16-2012, 5:36 PM
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Quote:
Originally Posted by jvh22a View Post
this is my first ar15 assembly and i got the nut on and did the tighten/loosen about 10 times aready. the fingers on the nut will always end right at the openning for the gas tube. at 50lbft the finger will be in the way as i tighten to max 80 it will almost clear. just a bit more.

in your opinion should i just tighten it down just a bit more? cause if i loosen the nut it i would be in the 30lbft range. and that is just a bit tighter then hand tight.

compensator is already welded on and gas block in place so dont want to remove those.





I would tighten a hair more .That would be ok.Did you forget to use never-sieze on the threads.?The stuff you put on brake pad calipers bolts.
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Old 12-16-2012, 5:36 PM
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Quote:
Originally Posted by jvh22a View Post
this is my first ar15 assembly and i got the nut on and did the tighten/loosen about 10 times aready. the fingers on the nut will always end right at the openning for the gas tube. at 50lbft the finger will be in the way as i tighten to max 80 it will almost clear. just a bit more.

in your opinion should i just tighten it down just a bit more? cause if i loosen the nut it i would be in the 30lbft range. and that is just a bit tighter then hand tight.

compensator is already welded on and gas block in place so dont want to remove those.





I would tighten a hair more .That would be ok.Did you forget to use never-sieze on the threads.?The stuff you put on brake pad calipers bolts.
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  #12  
Old 12-16-2012, 6:39 PM
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Thanks for all the help guys. I ended up about 94lbft and the gas tube lined up perfect. If I backed it off to the openning before, it would have only been about 15lbft.


List of parts used:
-Upper
PSA blem and all the other stuff on it like dust cover.
Bcm gas block
Rainier select barrel
Rainier xtc
Rainier evo 11 rail
Magul mbus
Fail zero bcg and hammer
Bcm mod4 charge handle

-lower
Aero precision lower
PSA lower parts kit
Mega arms trigger
Magpul Moe+ grip
Magpul str stock

Here some pics.








Going to try it out on Thursday at Angeles.


*** last question. Headpace was checked before I took the barrel nut off. Since I reinstalled everything and the torque was about the same as before should I be ok? I only checked with a "no go gauge". All parts are new, if that matters.
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  #13  
Old 12-16-2012, 7:35 PM
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94 ft/lbs?

Dude-- that is more than what my RIM needs to stay on the car. It's supposed to be 30-40 ft/lbs, IIRC.
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Old 12-16-2012, 9:15 PM
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Barrel nut torque does not change headspace. If you were ok before, you are ok now.
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  #15  
Old 12-16-2012, 11:45 PM
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Quote:
Originally Posted by phrogg111 View Post
Top end torque should never be above 40 foot pounds, and the range is more like 23-40 ft-lbs that you should be torqing it to!

Really, I've seen people using their AR-15s with the barrel nut torqued hand tight. If you're going up to 80 foot pounds, you're destroying the threads on your ALUMINUM upper receiver!
Not terribly good advice, phrogg. Whose specs are you referring to?

Barrel nut torque is 30-80 ft-lbs. or 35-80 ft-lbs., depending on whose manual you're using. While there's no way that the threads will be damaged using up to 80 ft-lbs of torque, 94 is a bit high Had the OP's barrel not already had the brake blind pinned in place, using some shims would have gotten that barrel nut into alignment without exceeding that upper torque limit. Unfortunately, that would require removing the barrel nut to install the shims... a little difficult in this case considering the already welded muzzle device.
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Old 12-17-2012, 12:35 AM
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I understand that 94 foot lbs is on the high end, but its either that or Back off to 10-15 foot lbs to get the last opennings to line up.
I'm no expert but there is no way I'm going go with 10-15 foot lbs. You can use 2 fingers to twist off the barrel nut at that low torque.

I just read about the shims and I would hate to have to cut off the new rainier xtc. But for the next build I will do this and not be in a hurry and weld the comp.

Also didn't want to cut the nubs off the nut. Just in case it helps keep the tube in line with bcg.
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  #17  
Old 12-17-2012, 5:15 AM
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Like I said. The USMC manual says to torque the barrel nut to 35 ftlbs (they also say do it a total of three times.) then if the hole doesn't line up, tighten to next hole. There is no mention of max torque. There is also not mention of oil or anti seize being used on the threads which will change your torque reading.
I'm going to insult some marine reading this on the board but that manual was written so that a trained monkey could do it right. I think you guys are over thinking this.
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Old 12-17-2012, 7:15 AM
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5. Position rifle barrel assembly (2) with alignment pin (6) up. Using barrel remover fixture (7), clamp rifle barrel
assembly (2) in vise.
NOTE
The slot should fit the alignment pin perfectly with very little or no rotational play present. Note the play in a new
rifle barrel assembly and new upper receiver assembly and use this as a guide.
6. Align upper receiver assembly (8) or (8A) using alignment pin (6) and the slot in upper receiver assembly (8) or
(8A). Install over end of rifle barrel assembly (2).
7. Wipe upper receiver threads clean and ensure there are no burrs. Apply molybdenum disulfide grease to the
threads before installation.

8. Engage threads of barrel nut assembly (9) with upper receiver assembly (8).
9. Using combination wrench (10) and torque wrench, torque barrel nut assembly (9) to 30 ft-lb (40.5 N-m).
Torque is measured when both wrenches are used together.

NOTE
Three times torquing procedure provides for a better thread fit and prevents barrel nuts from becoming loose.
Do not use the torque wrench for loosening.
10. Make certain all three drive pins on combination wrench are engaged with barrel nut assembly (91 Loosen and
repeat torque operation. Then loosen the barrel nut again.
11. Front sight post must be Installed. Loosen the vise and align the bore on a distant vertical target Center the
target In the bore from 12 o’clock through 6 o’clock The, front sight post should be on line and vertical with the
target. Tighten vise Adjust the rear sight windage until a proper sight picture is obtained on the vertical target
The rear sight aperture will be approximately In the center of the rear sight base If the rifle barrel assembly is
properly aligned in the upper receiver assembly
NOTE
If rifle barrel assembly (usually new) is not properly aligned In the upper receiver assembly (usually an old part),
excessive windage will be present and the upper receiver assembly will require replacement to obtain the proper
fit between the alignment pin and slot.
CAUTION
Do not torque over 80 ft-lb (108 N-m) while tightening the barrel nut assembly to the next hole, to allow for
proper alignment of gas tube.

NOTE
Do not attempt to hold the upper receiver assembly with a pry bar, however, If the rifle barrel assembly
turns In the holding fixture, a pry bar may be used through the front sight assembly base to help prevent
the rifle barrel assembly from turning In the holding fixture. Use care not to distort or bend front sight
assembly or retaining pins. Use "buddy system" to hold pry bar.
12. Torque the barrel nut assembly again to 30 ft-lb (40.5 N-m) while maintaining sight alignment. The barrel nut
assembly may be tightened beyond 30 ft-lb (40.5 N-m) to align the barrel nut assembly serrations for proper gas
tube clearance Never loosen the barrel nut assembly to align for gas tube clearance.

13. Check alignment of barrel nut assembly (9) with upper
receiver assembly (8). The front 8 inches (20.32 cm)
of a gas tube may be used as an alignment tool (see
Illustration). This Is Inserted Into the bolt carrier key
and then Inserted into the rear of the receiver. If the
parts of the barrel nut assembly are properly aligned,
the tool will pass freely and lay top dead center along
the top of the barrel. A number 15 twist drill (0.180
inch) may also be needed as an alignment tool. If
necessary, tighten barrel nut assembly to next hole to
allow proper alignment.

Sorry OP, sucks to be you, don't know what to tell you.....
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  #19  
Old 12-17-2012, 7:26 AM
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A new barrel nut is what? $8, $9?
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Old 12-17-2012, 9:11 AM
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Barrel nut is $14. And I would have to cut off the comp/brake.

In any case I'll try it out. Hope the receiver doesn't blow up on me.
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Old 12-17-2012, 10:28 AM
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The receiver's not going to blow up on you.
Worse case is you stretched the threads and a new barrel nut may not go on without some work.
Aluminum is funny that once it starts to let go it goes all at once. So if you over torqued the thread to the point of damaging the receiver the torque would get less every time you torqued it. i.e. the threads giving up.
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Old 12-17-2012, 10:45 AM
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You should be okay even with the 80+ Ft Lb of torque. I have a few builds that ended up going more than 80 Ft Lb for final torque. None of them have blown up on me, and in fact those tend to be more accurate than the ones that snug up at 40-50 Ft Lb.
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Old 12-17-2012, 10:49 AM
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surprised the index pin didnt shear off when installing a barrel and aftermarket free floating handguard setup. There was one barrel where I took it to right a hair above 35lb because it was so so close to being lined up perfectly, and the index pin broke off. In my experience the index pin broke off before the upper received index pin notch or barrel nut threading took any damage. Manufacturer sent me a new barrel with index pin and that didnt happen the second time.
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Old 12-17-2012, 10:51 AM
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Make sure your Optics mounted on your Receiver, not the Barrel. Most guys install it at the forward part of receiver.
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Old 12-17-2012, 11:27 AM
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Thanks for all the replies. Thiswill help out other noobs trying to put a rifle together.


My rds is mounting on the first notch of the rail. Forgot that the rail could be off. I'll move it back to the last notch of the receiver.

Again thanks for all the pointers.
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Old 12-17-2012, 11:28 AM
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Quote:
Originally Posted by MustangSteveGT View Post
surprised the index pin didnt shear off when installing a barrel and aftermarket free floating handguard setup. There was one barrel where I took it to right a hair above 35lb because it was so so close to being lined up perfectly, and the index pin broke off. In my experience the index pin broke off before the upper received index pin notch or barrel nut threading took any damage. Manufacturer sent me a new barrel with index pin and that didnt happen the second time.
That sounds like a damaged pin that just so happened to let go, not an over torque issue. common dowel pin requires 2600 lbs of force to shear
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Old 12-17-2012, 11:53 AM
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Quote:
Originally Posted by jvh22a View Post
I understand that 94 foot lbs is on the high end, but its either that or Back off to 10-15 foot lbs to get the last opennings to line up.
I'm no expert but there is no way I'm going go with 10-15 foot lbs. You can use 2 fingers to twist off the barrel nut at that low torque.

I just read about the shims and I would hate to have to cut off the new rainier xtc. But for the next build I will do this and not be in a hurry and weld the comp.

Also didn't want to cut the nubs off the nut. Just in case it helps keep the tube in line with bcg.
You should be okay, as kcstott says, the receiver isn't going to blow up on you. No need to cut off the brake to add shims at this point. Worst case, if you dismounted the barrel and remounted it, the threads would yield and change the torque in a given position. You were wise not to cut the nut, that's a Bubba solution.

Go out and shoot it!
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Old 12-20-2012, 9:52 PM
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This thread is full of win.
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Old 12-21-2012, 4:16 AM
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This thread is full of win.
That was completely unproductive. Please give us some insight as to what you would do or maybe suggest he bring it to you for a small fee. You seem to be the resident "expert" on this stuff since you own a business that does this work.

OP: since the muzzle device is already welded, I would take a small round file to the tooth an shave a bit off if you feel you need less torque, or if someone with the information/knowledge was to say it was unsafe. You would only be filing on a cheap part.
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Old 12-22-2012, 9:27 AM
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Please give us some insight as to what you would do
I would put a barrel nut indexing shim in.
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Old 12-22-2012, 9:29 AM
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Over torquing !! 30 -40 ft.lbs
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Old 12-22-2012, 12:46 PM
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I don't really see a downside to removing the tooth, you've got plenty and I doubt it has any utility in aligning the gas tube.

You could cut a shim so that it can sneak in between the barrel nut and barrel extension but if you don't have a shim, loosing a tooth is fast and cheap.

I doubt you are going to swap upper receivers so much that you cut off too many teeth to grab the barrel nut with an armorers wrench.

Now if you are a pro like Randall, you should have shims on hand and check before you pin the muzzle device but that doesn't mean that cutting off a tooth is a bad option.

I would not suggest installing a shim between the upper receiver and the barrel extension.
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Old 12-22-2012, 2:30 PM
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I don't really see a downside to removing the tooth, you've got plenty and I doubt it has any utility in aligning the gas tube.
The snap-in handguards key off the barrel nut and the handguard cap.
Having the barrel nut out of index will make it much more difficult to install the handguards.
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Old 12-22-2012, 3:09 PM
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Is the barrel nut for the LR308 different?
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Old 12-22-2012, 4:50 PM
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Yes, LR308 barrel nuts are a lot bigger.

Randall, I see your point about indexing a free float rail but not all index on the teeth.
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Old 12-22-2012, 5:14 PM
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No one seems to have hit on the issue of the bolt carrier being in alignment with the gas tube. The carrier key needs to slide over the tip of the gas tube as the group moves forward into battery.
If the teeth of the barrel nut do not provide enough support to each side, say by grinding off a tooth of the nut, the gas tube is no longer limited from moving too far out of alignment. It could impact the gas key, instead of sliding into the gas key. Also the issue Randall hit on, being the use of handguards that index off of the barrel nut. If the nut is off center, those type handguards do get funky as well.

Since the gas tube was not in alignment with final torque being too much:
1-Use a shim between the barrel nut and face of the receiver.
2-Lightly remove a small amount of metal from the front face of the receiver to gain more of a rotation to the nut. Hitting the face with a stone will remove a small amount of finish and could be just enough to make it right. Don't stone it crooked.
3-Go gorilla tight on the nut to get it to the next notch. Simple fix and may not cause an issue if the tooth just needed a small amount of distance to get in alignment.

The torque readings are there to provide a reasonable guide to the armorer on how tight to make the barrel nut. Some folks will just crank on the wrench and try to bend the receiver to make it "tight", some will not give it enough muscle and end up leaving the barrel nut enough room to work its way loose.

I will guess that the OP is good to go with his barrel by just using a bit more muscle to get that barrel nut aligned. It didn't seem to need much more of a turn on the wrench to get it into the sweet spot.

How did the rifle run?
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Old 12-22-2012, 5:35 PM
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Well the upper has little fingers keeping the gas tube in place, I doubt the barrel nut teeth have anything to do with locating the gas tube and my experience trial fitting AR uppers before applying final torque, minor misalignment of the barrel nut (as in less than finger tight) won't cause the gas key to bind or anything.
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Old 12-24-2012, 5:20 AM
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Quote:
If the teeth of the barrel nut do not provide enough support to each side, say by grinding off a tooth of the nut, the gas tube is no longer limited from moving too far out of alignment. It could impact the gas key, instead of sliding into the gas key.
Wrong.
The receiver locates the gas tube.
The barrel nut should never be in contact with the gas tube.
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Old 12-24-2012, 8:29 AM
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Great info Randall!
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Old 12-24-2012, 8:29 AM
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Quote:
Originally Posted by ar15barrels View Post
Wrong.
The receiver locates the gas tube.
The barrel nut should never be in contact with the gas tube.
That means the teeth are just there for the purpose of tightening the barrel nut.
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