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Posted: 8/27/2009 5:49:31 PM EDT
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I was thinking that since this will be my first upper build that I'd get a torque wrench to use (along with a PRI barrel nut wrench) and make sure that I'm at least at the bottom of the torque spec...35 lbs or so....This will be a Larue 12.0 install.
BUT, I know that there will be an increase in the torque moment by using this setup and am wondering if the recommended spec of 30-80 ft/lbs is accounted for in doing so....OR, will I actually need to factor in the increased leverage by measuring the different distances between the torque points? OR, just say the hell with that and not use a torque wrench? 
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The specs include the offset for the barrel nut wrench.
No need to recalculate. Set your torque wrench to minimum torque for the first two tightenings. Then set it to the max (or a few pounds under - I set mine to 75) for the final when aligning the gas tube hole, to make sure you don't over torque. |
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The specs include the offset for the barrel nut wrench. No need to recalculate. Set your torque wrench to minimum torque for the first two tightenings. Then set it to the max (or a few pounds under - I set mine to 75) for the final when aligning the gas tube hole, to make sure you don't over torque. And grease the threads. |
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I've used a breaker bar to put mine together. Don't forget the anti-seize or moly lube. Get it hand tight, then to the next full tooth just to make sure it's seated against the upper. Loosen, then repeat for final tight. If you are using a wrench, don't sweat the little bit of extra leverage you'll get. I don't think you'll get anywhere near 80 ft-lbs, unless you try to turn it another tooth past these directions. Remember - the bolt seats to the barrel extension, not the upper receiver. There's no need for gobs of precision torque. |
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There IS, however a need to make sure you don't strip the upper's threads, or torque the nut so tight that it takes an impossible amount of leverage to remove it. Use a torque wrench-an acceptable one can be had from Harbor Freight for $20. And use a wrench that engages more than 3 teeth for a more secure hold on the nut-I use the DPMS Multi-Tool. The DMPS tool's torque wrench socket is in the same place relative to the barrel wrench engagement as the GI wrench's socket, so torquing with this tool is accurate.
I've used a breaker bar to put mine together. Don't forget the anti-seize or moly lube. Get it hand tight, then to the next full tooth just to make sure it's seated against the upper. Loosen, then repeat for final tight. If you are using a wrench, don't sweat the little bit of extra leverage you'll get. I don't think you'll get anywhere near 80 ft-lbs, unless you try to turn it another tooth past these directions. Remember - the bolt seats to the barrel extension, not the upper receiver. There's no need for gobs of precision torque. |
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Don't forget the anti-seize or moly lube. So you can use anti-seize instead of moly grease? 
I will be installing a barrel on my first AR tomorrow and I have plenty of anti-seize. Do I really need moly grease??? Can anyone else confirm this? Well, Molybdenum Disulfide grease is the proper product. That will take the temperature and stay in place for years, so the rifles can be modified or the barrel replaced. If you never expect the rifle to be disassembled, I suppose anti-seize or even axle grease would be OK for assembly. |
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Don't forget the anti-seize or moly lube. So you can use anti-seize instead of moly grease?
I will be installing a barrel on my first AR tomorrow and I have plenty of anti-seize. Do I really need moly grease??? Can anyone else confirm this? Well, Molybdenum Disulfide grease is the proper product. That will take the temperature and stay in place for years, so the rifles can be modified or the barrel replaced. If you never expect the rifle to be disassembled, I suppose anti-seize or even axle grease would be OK for assembly. As far as I know anti-seize is used for the intent purpose of things being able to "be" removed without problems, I could be wrong but maybe someone else could clarify this. I use it on wheel lug-nuts just for that reason. So I don't have to take out and hammer with the impact. |
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Make sure you know what you're doing and get a good wrench, good anti-seize compound (and remember to put it on the face of the receiver threads) and don't over torque it. Based on my experience putting on a barrel...have a professional do it for you. (Note the mangled barrel nut teeth).  |
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you must have had a bad experience. I got mine on with little problem. I had a different barrel and receiver combination which put the barrel nut RIGHT in the middle of the gas hole of my upper receiver but ithother than that it was easy. I was going to file down the face of the receiver a little bit but figured I didn't need it torqued as much as I COULD. Backed off a couple times and torqued it enough to get the gas tube through and have the barrel in place snug.
I got the tool from NCStar and it has everything you'd need and some more. |
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I was thinking that since this will be my first upper build that I'd get a torque wrench to use (along with a PRI barrel nut wrench) and make sure that I'm at least at the bottom of the torque spec...35 lbs or so....This will be a Larue 12.0 install. BUT, I know that there will be an increase in the torque moment by using this setup and am wondering if the recommended spec of 30-80 ft/lbs is accounted for in doing so....OR, will I actually need to factor in the increased leverage by measuring the different distances between the torque points? OR, just say the hell with that and not use a torque wrench? Don't forget to use some sort of fixture to hold the upper receiver . There are several on the market ,I use the clam shell type for 5.56 & the Block for 308's. ( because they don't make the clam shell type for 308 ) Do not use bbl. vice blocks . |
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The specs include the offset for the barrel nut wrench. No need to recalculate. Set your torque wrench to minimum torque for the first two tightenings. Then set it to the max (or a few pounds under - I set mine to 75) for the final when aligning the gas tube hole, to make sure you don't over torque. Are those specs good for the PRI wrench as well?...I guess I could just measure both tools and see if they have the same offset....Thanks everyone for the help. |
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btt for further info and input... You are way over thinking this. The barrel nut torque is not a "tight" spec. It's sloppy as hell, (i.e. 30-80ft-lbs). What controls it is the position of the teeth, to clear the gas tube. I don't even use a torque wrench. I have and 18" breaker bar, so 20 pounds of pressure out at the end gives 30 ft-lbs or torque. I know how heavy 20 pounds feels, so that's how hard I push on the end of the breaker bar. And that is tight enough for the spec. Then, I look at the teeth, and keep applying force and testing the gas tube. When it fits in nice and square, I am done. Remember, the barrel nut cannot come loose because of the gas tub. The bolt engages the barrel extension. So as long as the barrel is wobbling in the upper receiver threaded sleeve, the gun will operate perfectly well. Now, go build your rifle. 
ETA: There is one and only one tooth on the barrel nut that will properly align for the gas tube (let's call it the "golden tooth"). If you tighten one tooth before the golden tooth, then the nut will be obviously too loose. If you attempt to tighten one tooth past the golden tooth, then you will have broken something or ripped the skin off the bones in your hand 
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