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Posted: 1/23/2011 5:25:50 AM EDT
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Howdy ARFCOM,
After getting the components to assemble my AR15 Dissipator Upper a while back, last night I finally had the time to torque the barrel nut and install the gas tube, with a KAC M5 RAS coming on Monday. I was tightening the barrel nut, and got it simply as far as I could (no torque wrench, as I've heard of people doing without them, and I'm not a weakling), and it was a degree or less off from the gas tube port on the receiver. Well, it looked so close, I tried putting it in there, and surely, I was able to do that as well as get it in the gas block without any trouble. 
However, as I was putting the BCG in there, I noticed it was a little harder than without the gas tube. I looked inside and saw this: 
So, my question is, should I remove the gas tube and try to torque the barrel nut that fraction more, or will this not cause a problem? Considering the gas tube is a rather pliable metal (it's already bent under the handguards), perhaps the gas key will simply make it straight over time. Am I wrong? Is this a big no-no? Thanks to any and all in advance. |
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You could technically bend that tube a bit so it is straight right there, wouldn't hurt anything....
but if i was you.. i would get a torque wrench and do it right. I don't know where you "heard" about people doing it without proper tools but this is something you hold in your hands, close to your face... that causes mini explosions... something you really want to hillbilly during assembly? Assembling the barrel nut without the proper tools in the proper way is not safe, and not "ok"... doing crap like that presents a needless danger to yourself and others. Do it right youll never have a problem. |
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Thanks for the advice, guys.
I was able to get the barrel nut move a little more with some elbow grease, and then lubed the outside of the gas tube slightly where it enters the gas key, and there is virtually no difficulty in me getting it to cycle. The only real resistance is the cam pin. Before I fire it, I will definitely try to tighten it even more. I still don't have a lower for this yet, so I won't be doing anything stupid so soon. |
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Torquing the barrel nut means setting the torque wrench on the FINAL twist to 85 pounds, and not EXCEEDING it. Twist it until it's straight, or, as you see, the tube is crooked and won't center on the gas key. That's much more important than the torque, because it's all about lining things up, not having some spec met. It may not go over 40 or 50. Depends on the thread indexing, not the torque.
You tighten it three time at 30 pounds to work the burrs off the thread, then get it lined up without stripping them. The 85 pound setting keeps you from doing that. If it just won't go, use a lapping square and take off a few thousandths, and try again. Once the tube is in, it holds the nut. Check it when you clean it to see it's not being tweaked. Too many read numbers and don't understand the reason for the procedure. |
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Another way to check the gas tube alignment is remove the bolt from the carrier and the charging handle. You will be able to see and feel any friction between the gas key and tube a little easier when you slide the carrier back and forth.
The torque wrench will only be useful to make sure you are in the range of 30-80 ft lbs. The actual reading will depend on where the nut lines up. When the nut is slightly off alignment it creates the slight angle you were seeing. Over time it may cause wear on the gas tube where it rubs the key, but will work. It sounds like you got it fixed. Schuster makes a rod that checks the alignment, sort of a go/no go gauge for the nut alignment. Not worth the price if you are only doing one. Handy if you are doing several. Midway sells them. Not important, but the tube doesn't hold the nut. The properly aligned nut holds the tube straight. The tube will keep the nut from spinning off if it is loose, but if the nut is loose it is not because the gas tube didn't' hold it. It 's because the nut wasn't tightened properly. |
I would be sure to torque it. My last one we ended up torquing it all the way to the max torque before getting it in place and that was after loosening it 4-5 times and some grease on the threads. Unlike other firearms, the AR actually needs to be well within spec or it will be a problem. 
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Barrel nut torque should be at least 30 foot pounds but no more than 80. It doesn't require a torque wrench. Now, alignment of the gas tube notch is tricky, it looks like you should try again, multiple attempts will seat the threads, allowing the next notch to index properly. Proper grease (moly only) also helps, it can reduce the torque necessary to make it to the next notch. |
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Quoted:
You could technically bend that tube a bit so it is straight right there, wouldn't hurt anything.... but if i was you.. i would get a torque wrench and do it right. I don't know where you "heard" about people doing it without proper tools but this is something you hold in your hands, close to your face... that causes mini explosions... something you really want to hillbilly during assembly? Assembling the barrel nut without the proper tools in the proper way is not safe, and not "ok"... doing crap like that presents a needless danger to yourself and others. Do it right youll never have a problem. You don't "need" a Torque wrench, but I suggest using one. I've used a breaker bar in a pinch, and it works just fine. |
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Quoted:
Barrel nut torque should be at least 30 foot pounds but no more than 80. It doesn't require a torque wrench. Now, alignment of the gas tube notch is tricky, it looks like you should try again, multiple attempts will seat the threads, allowing the next notch to index properly. Proper grease (moly only) also helps, it can reduce the torque necessary to make it to the next notch. Quoted:
Torquing the barrel nut means setting the torque wrench on the FINAL twist to 85 pounds, and not EXCEEDING it. Twist it until it's straight, or, as you see, the tube is crooked and won't center on the gas key. That's much more important than the torque, because it's all about lining things up, not having some spec met. It may not go over 40 or 50. Depends on the thread indexing, not the torque. You tighten it three time at 30 pounds to work the burrs off the thread, then get it lined up without stripping them. The 85 pound setting keeps you from doing that. If it just won't go, use a lapping square and take off a few thousandths, and try again. Once the tube is in, it holds the nut. Check it when you clean it to see it's not being tweaked. Too many read numbers and don't understand the reason for the procedure. Complete BS. The max torque spec is a completely irrelevant number. Torque it to 30 foot pounds and then continue on until the next notch. |
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FWIW...don't rely solely on lubricating the gas key to keep it from binding on the tube. The tremendous heat from the bleed gas will quickly burn off anything on that area, unless it is lined up you wil have cycling problems or eventual damage from the gas key whacking the tube. Bending the tube is a hack way to fix the problem. Do it correctly, and you save a lot of headaches down the road.
I align the tube until the bolt carrier will slide effortlessly over the tube. No lube, no bending. I use a torque wrench just to have an idea of how much force I am placing on the barrel nut, especially when I am building a rifle for someone else. It's a different ballgame when you are doing it as part of your business, doing it right the first time is the only way a firearm leaves my shop. Call it OCD or whatever, right is right. Anything less and you are asking for problems. |
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Quoted:
Schuster makes a rod that checks the alignment, sort of a go/no go gauge for the nut alignment. Not worth the price if you are only doing one. Handy if you are doing several. Midway sells them. Not important, but the tube doesn't hold the nut. The properly aligned nut holds the tube straight. The tube will keep the nut from spinning off if it is loose, but if the nut is loose it is not because the gas tube didn't' hold it. It 's because the nut wasn't tightened properly. Go buy a number 15 twist drill (0.180 inch) it's a perfect alignment tool, and a LOT cheaper than the Schuster tool. |
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Quoted:
Barrel nut torque should be at least 30 foot pounds but no more than 80. It doesn't require a torque wrench. Now, alignment of the gas tube notch is tricky, it looks like you should try again, multiple attempts will seat the threads, allowing the next notch to index properly. Proper grease (moly only) also helps, it can reduce the torque necessary to make it to the next notch. THIS!!! |
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Quoted:
Quoted:
Barrel nut torque should be at least 30 foot pounds but no more than 80. It doesn't require a torque wrench. Now, alignment of the gas tube notch is tricky, it looks like you should try again, multiple attempts will seat the threads, allowing the next notch to index properly. Proper grease (moly only) also helps, it can reduce the torque necessary to make it to the next notch. THIS!!! OK genius... How do you meet and minimum and not exceed maximum without a torque wrench? |
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Quoted:
Quoted:
Quoted:
Barrel nut torque should be at least 30 foot pounds but no more than 80. It doesn't require a torque wrench. Now, alignment of the gas tube notch is tricky, it looks like you should try again, multiple attempts will seat the threads, allowing the next notch to index properly. Proper grease (moly only) also helps, it can reduce the torque necessary to make it to the next notch. THIS!!! OK genius... How do you meet and minimum and not exceed maximum without a torque wrench? If you can't feel between 30-80 ft lbs, then you can't. No shame in that. |
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Complete BS. The max torque spec is a completely irrelevant number. Torque it to 30 foot pounds and then continue on until the next notch. This is an incorrect statement. Although it is VERY rare, it is possible to be unable to get the tube slot to align over 30ft/lbs, or by the time you reach 80ft/lbs. Then it is time for a spacer, or a new part. Please do not tell folks that a torque spec is "Irrelevant". There are new to AR folks here that can break there stuff on advice like that. Thank you. 
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Quoted:
Quoted:
Complete BS. The max torque spec is a completely irrelevant number. Torque it to 30 foot pounds and then continue on until the next notch. This is an incorrect statement. Although it is VERY rare, it is possible to be unable to get the tube slot to align over 30ft/lbs, or by the time you reach 80ft/lbs. Then it is time for a spacer, or a new part. Please do not tell folks that a torque spec is "Irrelevant". There are new to AR folks here that can break there stuff on advice like that. Thank you.
Barrel nuts come with shims so if you can't tell the difference between 30 and 80 foot pounds then something is wrong with you. My statement stands as long as op has common sense....if it won't line up then use a shim and try again etc. |
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Quoted:
Quoted:
Complete BS. The max torque spec is a completely irrelevant number. Torque it to 30 foot pounds and then continue on until the next notch. This is an incorrect statement. Although it is VERY rare, it is possible to be unable to get the tube slot to align over 30ft/lbs, or by the time you reach 80ft/lbs. Then it is time for a spacer, or a new part. Please do not tell folks that a torque spec is "Irrelevant". There are new to AR folks here that can break there stuff on advice like that. Thank you.
Spacers, new parts? This is better than the guy who said he could properly torque the nut without a torque wrench. |
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You can actually go down to the True Value Hardware store and get solid rod the same size as your gas tube and install it in the upper from the back where the buffer and carrier go with out the charging handle and use it to tighten the barrel nut and index it where it should go... I made one Ill post a Pic when I get home but I would straighten out the gass tube before you wear the tube and the gass pickup on the bolt..... |
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Quoted:
Quoted:
Quoted:
Complete BS. The max torque spec is a completely irrelevant number. Torque it to 30 foot pounds and then continue on until the next notch. This is an incorrect statement. Although it is VERY rare, it is possible to be unable to get the tube slot to align over 30ft/lbs, or by the time you reach 80ft/lbs. Then it is time for a spacer, or a new part. Please do not tell folks that a torque spec is "Irrelevant". There are new to AR folks here that can break there stuff on advice like that. Thank you.
Barrel nuts come with shims so if you can't tell the difference between 30 and 80 foot pounds then something is wrong with you. My statement stands as long as op has common sense....if it won't line up then use a shim and try again etc. This is a new one on me .... so who exactly makes these barrel nut shims? The only way I know to get a barrel nut to index the gas tube correctly that will not between the proper torque values is either change the nut or lap the upper. 
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| I once had a slightly irregular barrel nut where every tenth tooth was slightly bent and the tube hit on one of these bent tooth. so at 65 lbs I marked the tooth and cut it at its base noched the area where the tube went trough and used 70 lbs with locktite and havent seen any problems with my sons rifle yet.... But I should have had Sarco replace the barrel nut but my son really wanted to try out his new AR.... Again as I said on the top post you can get round bar stock at True Value Hardware in the metal section or in the hobby section and make your own tool to make sure its straight.... |
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I am not trying to be bellicose but I will reassert my opinion that the upper torque value is irrelevant. Hear me out...
There is a little math behind a torque wrench. Just because you own one, doesn't mean you know how to use it. I am sure there will be a number of members who run back in and say they know the math and always use it, sure you do... When you put an extension on a torque wrench, like a crow foot or armorers wrench, the torque applied to the barrel nut increases, since the lever arm increases. N = Normal length of torque wrench (Center of handle to center of drive head) E = Extended length of torque wrench (Center of handle to center of barrel nut) A = Actual torque applied to the barrel nut T = Torque setting of the wrench A = (TN) / E Given a 16 inch torque wrench with an inch and quarter extended length and a desired actual torque of 80 ft lbs, what is the torque setting on the wrench? 74 ft lbs Now things get interesting. What if you move your hand off the center of the wrench by? 1 inch lower requires a torque setting of only 70 ft lbs 1 inch higher requires a torque setting of 79 ft lbs How important is it to know the center of your handle? Another important factor to remember is torque vector. The torque wrench must remain parallel with the armorers wrench and the drive socket must be in the center of the armorers wrench. Except for an old school Colt barrel wrench I have, I could not find one wrench that had a drive socket on the center of the wrench. Changing either of those variables will change the final torque value. While I wouldn't recommend putting a big torque value on the barrel nut, 100 ft lbs or even 125 won't hurt a thing. Who's next... |
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"Barrel nuts come with shims"––––this is a new one for me also, out of over 2 dozen builds and many mpre redone or worked on I have yet to have or see a "barrel nut shim", or have the need for one.
"with locktite"––––––––––––––––––––––––––––friends don't let friends use locktite on guns...how many times have we read here of new members here having problems removing a barrel nut that someone may have used locktite on. Use the proper lubricant, NOT LOCKTITE....<><....:) |
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With standard encapsulated barrel nut wrenches, it is nearly IMPOSSIBLE to get 80 foot pounds on the barrel nut. That is lug nut tight and most lug wrenches are longer than the barrel nut wrench. If you cannot get the notch to align, back off the nut and try again. The uppers are hard anodized, this is a fairly brittle conversion coating which will compress and set a few thousandths. If you are still having problems, LIGHTLY sand the front of the upper where the collar of the barrel extension seats. Don't remove the anodization but just polish it. You need to use silicon carbide paper, 400 grit or finer. Remember, polish, not remove anodization. Yes, you could shim the barrel extension collar where it seats on the upper. But a half tooth is just a hair over a half a thousandth of an inch. Find shims that thin? Impossible. |
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