I have a new M4 style barrel that I’m trying to install on my AR-15.  I’m using the “Assemble you own” instructions in the sticky thread.  I pretty much understand everything, but am still having trouble.  I have a DPMS armorer’s wrench.  Step 11 says to “Inspect the barrel nut lugs, and continue to tighten the nut until the lugs line up with the gas tube hole in the receiver”.  Using my armorer’s tool, I can tighten it to align one slot very easily using just one finger.  In another thread it says the torque should be “31 Ft. lbs Minimum, not to exceed 80 Ft. Lbs. to align the next slot in the barrel nut”.  The one that I’m on certainly doesn’t feel like 31ft-lbs, so I tried to go to the next one.  In the process I broke off one of the teeth on the barrel nut.  There are plenty more left, but even if I turn the wrench really hard, it won’t make it around to the next slot.  I have a torque wrench.  How do I use my torque wrench in combination with the armorer’s tool to take a measurement?  I want to be sure that the slot that I can easily get to is > 31ft-lbs.  Are the torque values of 31ft-lbs and 80ft-lbs measured from the center axis of the barrel or are they measured from the ½” drive square in the armorer’s wrench?  If they are measured from the center axis of the barrel, what are the conversion factors for using the DPMS armorer’s wrench?

tighten
loosen
tighten
loosen
tighten

then turn it a little to align next gas tube hole, i have never used a torque wrench and it all have worked good for me.

I did that already.  It just seems to be too easy to get to one slot and yet I can't get to the other.  If someone could explain how to use the torque wrench in combination with the armorer's tool, I can take torque measurements to be sure.

Quoted: I did that already.  It just seems to be too easy to get to one slot and yet I can't get to the other.  If someone could explain how to use the torque wrench in combination with the armorer's tool, I can take torque measurements to be sure.

See that square hole in your armorer's wrench, stick the torque wrench into it......

Mike

ps - as noted aboveI have never used one on any of mine either......, not necessary

Mike, I know how to do that.  What I don't know is if the torque is measured from that square hole or from the barrel axis.

Quoted: Quoted: I did that already.  It just seems to be too easy to get to one slot and yet I can't get to the other.  If someone could explain how to use the torque wrench in combination with the armorer's tool, I can take torque measurements to be sure. See that square hole in your armorer's wrench, stick the torque wrench into it......have

Ditto here

I did the same thing last night.  I did the old tighten, loosen, tighten, loosen etc and it just bearly lined up on the next hole.  I had more trouble with the frigin' delta ring, thank goodness I had an extra gas tube.

Mike

P.S.  I did'nt use a torque wrench, I hope I don't blow myself up.

Did you use any lube on the barrel nut?  The first couple I built I put together dry and it was a bitch.  A little lube helped.  When you reduce the interface resistance on the thread to thread contact I believe you get a better feel as to how much force you are using.  On one of my early builds I was stuck exactly where you are.  I hosed the whole think down with CLP and it was a piece of cake to get to the next slot.  Now I use never seize.

Hope it helps.

Torque is measured in foot  pounds, so I would assume the torque wrench is calibrated based on its length. If you lengthen the wrench which would happen by attaching the barrel wrench then you
would be torquing more than the reading.  

Quoted: If you lengthen the wrench which would happen by attaching the barrel wrench then you would be torquing more than the reading.

Exactly.  That's why I need to know if the torque measurement is made from the axis of the barrel or from the point where the torque wrench attaches to the armorer's wrench.

Yes, I did lube the threads on the receiver.

I would almost bet it would be from the armorers wrench, I dont know how you would get the torque wrench into the middle of the barrel. In fact here is a link to a photo on here of a guy building an SPR useing the torque wrench like that.

pic

DM1975, I bet that you're right, I just don't want to make any incorrect assumptions.  If the specifications are made from the barrel axis, then there should be a conversion factor and nobody seems to have such a figure.

I broke down and called DPMS since they made the armorer's tool that I'm using.  I spoke with a very helpful guy named Shane.  He told me that the torque specification is measured from the 1/2" drive square hole.  Now I should be able to determine if I have torqued the barrel enough.  I'll let ya'll know how it goes.

I have the barrel installed correctly.  It took approximately 69.5ft-lbs.  

Torque wrench... You guys are funny.

Never used one, and I do own one.

Bret, did you go to the "next hole", the one past finger tight?

I got the to the next slot.  The one just past finger tight was less than 30ft-lbs.  I'm an engineer, so I like things like specification ranges and torque wrenches.  It helps me to know that I did things right.

Besides, if you don't have a torque wrench, how do you tighten the lug nuts on your car wheels?

the torque value you set your wrench to is valid for the length of the torque wrench from the end of the handle to the drive at the other end, just remember to keep the armorers tool at a 90 degree angle to the torque wrench. If the tool extends past the drive, making the lever longer, you would have to use the torque conversion formula to figure out what new setting to set the wrench to. I have torqued in some crazy small spaces on UH-60s but so far I have managed to avoid doing any math!

Quoted: I got the to the next slot.  The one just past finger tight was less than 30ft-lbs.  I'm an engineer, so I like things like specification ranges and torque wrenches.  It helps me to know that I did things right. Besides, if you don't have a torque wrench, how do you tighten the lug nuts on your car wheels?

When I do barrel installs, it's all by feel. If that slot felt a little less than 30ft/lb, I just crank to the next one. It's not like you have a lot of choice, you're limited by the slots for the gas tube.

My lug nuts? The old fashion way. Star pattern, again by feel.

Remember, you engineers make the rules that us mechanical types don't necessarily follow.

I just installed my first barrel last night.  Basically the same issue.  The first hole in the barrel nut would line up finger tight, at 30 pounds be smack in the middle of the point of the next hole.  Even though I was using a torque wrench I really didn't have a choice and had to get it to the next hole.  It wound up being in the high 50pound range.  I loosened and tightened about 10 times and using high temp wheel bearing grease.

I found that using the USGI tool was easier than using a DPMS multi tool.

Quoted: tighten loosen tighten loosen tighten then turn it a little to align next gas tube hole, i have never used a torque wrench and it all have worked good for me.

+1

The first barrel I did was a bitch, in that it took a lot of force to get it to the next slot, but I ended up getting it close enough and it works great.  The other two barrels I have done have been much easier, and lined up perfectly while being nice and snug.