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Posted: 10/7/2003 2:37:49 PM EDT
Yojimbo just asked this question and the numbers that he got were 80'lbs to 89'lbs. A book I have "build your own AR15" by Duncan Long says that 35-45 foot lbs is the correct torque. I also just received the armorer's video from Bushmaster and they say 35-40 foot lbs is correct. Both of these sources are using a armorer's wrench of course.
This is my question with the pivot point so far back from the barrel nut on a armorer's wrench are you gaining enough of a leverage advantage to actually torque the barrel nut to 80lbs? And if this is the case ppl torqueing to 80lbs are really torqueing to 160lbs right???
My barrel comes tomorrow thanks for any help..
Link Posted: 10/7/2003 5:16:08 PM EDT
There is no magic torque figure. What is important is (1) the barrel assembly not be loose on the upper, and (2) the notch lines up to allow the gas tube to pass through into the upper without binding, (3) that you not overtighten and strip the threads. They recommend a minimum of 31 ft-lb, and then continue to tighten until you achieve alignment of the notch. This is USUALLY easily done without exceeding 80 ft-lb. Have you ever in your life tightened nuts and bolts? Can you feel when they are tight, that the parts will not come loose? Good. Forget the torque wrench. Use a "breaker bar" with 1/2" drive and barrel wrench. Use an "Action Block" (make sure you use the included insert inside the upper receiver). Do NOT use barrel vise jaws. A good vise (at least a 4", 5" is better) that is sturdily mounted is a must. Lighly lubricate the threads on the upper with some ordinary wheel bearing grease, NOT Neversieze. That is gritty, has metal particles in it. Snug up the barrel nut, and check for gas tube alignment. Do NOT jerk on the breaker bar to nudge it over more, smooth, steady pressure is the key. If you insist on using barrel vise jaws because "that is what it says in the Army manual", and later find that the front sight tower is canted over, don't come whining to me, I don't care, I warned you... it's your problem. Use barrel vise jaws for installing/removing flash hiders, muzzle brakes, compensators... not the action block. See comments above about canted front sight tower. "armorer's video from Bushmaster and they say 35-40 foot lbs is correct" If you get gas tube alignment at 35-40 ft-lbs it is by sheer chance. Maybe you will, as likely that you won't. If you INSIST on using the torque wrench, and obtain gas tube alignment at 30 ft-lb, quit while you are ahead. Once you get up to at least 30 ft-lbs, set the torque wrench aside and don't look at it again. Use the breaker bar, and go to the next notch to align the gas tube. "This is my question with the pivot point so far back from the barrel nut on a armorer's wrench are you gaining enough of a leverage advantage to actually torque the barrel nut to 80lbs? And if this is the case ppl torqueing to 80lbs are really torqueing to 160lbs right???" Don't worry about it.
Link Posted: 10/7/2003 5:41:09 PM EDT
Thanks for the help that makes me feel allot better about the process..
Link Posted: 10/7/2003 7:04:58 PM EDT
A_Free_Man is right on the money with his post. But...I use antisieze on the threads, I may want to remove that barrel in the future.
Link Posted: 10/7/2003 8:55:38 PM EDT
Thanks P806. Any recommendation for type or brand of antiseize?
Link Posted: 10/8/2003 1:03:52 AM EDT
I think where the 80lb. figure comes from is the US Marine Corps Tech manual, which states an upper torque limit of 85 ft-lbs. I could be just talking out my butt, but last time I checked that manual was downloadable from right here at AR15.com. I'm just too lazy to download it again. Truth is, when I assembled my upper, what A_Free_Man posted is pretty much what I did, only slightly differently. Tighten to 30, doesn't line up...give it a little push...lines up almost...loosen...almost all the way off...tighten...almost lines up...loosen...almost all the way off...tighten just a smidge more (Smidge is a technical term meaning "more than last time but not so much as to really look like an idjut")...and it lines up. BINGO! Job well done. Insert gas tube happily knowing that you've done this part right. Assemble Rifle. Go to range. Enjoy shooting something you built from a box of parts. Repeat as funds permit. Panz [bounce]
Link Posted: 10/8/2003 10:06:55 AM EDT
Neversieze IS the brand name of an anti-sieze compound. If you insist on using it here, mix a little glob of it with ordinary wheel bearing grease, about 2 parts grease to one part Neversieze. This is messy, nasty stuff, and you will need to degrease the area afterwards or you will be getting that stuff all over the place (looks like silver paint) for months. I have not found a need for it on the AR15 barrel nut. Just wipe a thin coat all the way around the threads of the upper receiver, and a little on the inside on the nut, remove excess.
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