AR15.Com Archives
 What is the definitive torque value for a carbine buffer tube nut? Some say inch lbs & others ft-lbs
jws360  [Member]
12/21/2008 8:30:57 PM
I am a bit confused. I have a pre ban lower which I intend to install a carbine stock on. Since I don't want to muck anything up or use too little/too much torque I did a little research. Unfortunately, that got me a little confused.

Some sources here say the nut should be 38-42 +/- INCH pounds, while others say 38-42 or so FOOT pounds. In the FAQ and posts here I see a notation for inch-lbs. Brownells video site, however, says foot lbs.

Obviously there is a VERY big difference between the 2. Too little torque & it falls of. Too much & one can snap something & do irreparable damage.

Is there a definitive answer or am I missing something? I prefer to do things 100% correct and not risk anything.

Thanks in advance.

jws360  [Member]
12/21/2008 8:59:42 PM
I came across another site that claims the INCH lbs figure is a misprint & it is indeed FT lbs.

Here is the site. Can't vouch for it, though:

http://sigforum.com/eve/forums/a/tpc/f/630601935/m/2011082831
puskrat  [Life Member]
12/21/2008 9:10:14 PM
Technical Manual
35-39 lb ft. When tool and torque wrench used together.

page 199

Also, I have installed three stocks, never measured the torque.
RacerXXL  [Team Member]
12/21/2008 9:15:37 PM
I hate this manual took me 30 minutes to find this, I suck

UNIT AND DIRECT SUPPORT MAINTENANCE MANUAL
ARMY TM 9-1005-319-23&P
AIR FORCE TO 11 W3-5-5-42
Supersedes Copy Dated August 1987

3-16. LOWER RECEIVER AND RECEIVER EXTENSION ASSEMBLY (CONT).
d. REASSEMBLY (CONT)
CARBINE ONLY

6G. Using the special tool (Item 12, app C) tighten the locking nut (5.5) until snug.
6H. Using the special tool (item 12, app C), and torque wrench, torque locking nut (5.5) to 40 ±2 inch pounds.
6J. Stake the receiver end plate (5.6) in 2 places across from the notches in the locking nut (5.5).
RacerXXL  [Team Member]
12/21/2008 9:19:21 PM
Edit for clarity
j3_  [Team Member]
12/21/2008 9:19:24 PM
Originally Posted By puskrat:
Technical Manual
35-39 lb ft. When tool and torque wrench used together.

page 199

Also, I have installed three stocks, never measured the torque.


That manual is where the confusion comes from as it list the nut as inch pounds.


http://www.coltcanada.com/techpubs.htm
this is alink to the Colt manual. Page 3-2-41 an 42 of the maintenance manual list it as foot pounds.
RacerXXL  [Team Member]
12/21/2008 9:36:09 PM
After looking at it some more I would have to say the manual I quoted is in error and J3_ is correct and Puskrat is referencing the torque spec for a rifle buffer tube spec.
jws360  [Member]
12/21/2008 10:01:05 PM
Almost glad to see I am not the only one confused. Just to make 100% sure, the correct figure is FOOT-POUNDS, correct?

Maybe someone with more authority here can make this part of a sticky so as to correct an apparently longstanding issue.
GHPorter  [Team Member]
12/21/2008 11:05:24 PM
Originally Posted By jws360:
Almost glad to see I am not the only one confused. Just to make 100% sure, the correct figure is FOOT-POUNDS, correct?

Maybe someone with more authority here can make this part of a sticky so as to correct an apparently longstanding issue.


Nope, it's the other way around. A carbine (adjustable stock) tube's lock nut (castle nut) is torqued to 40±2 INCH POUNDS. Using the other units on the castle nut could strip the tube out of the back of the lower, ruining the lower.
j3_  [Team Member]
12/22/2008 5:32:27 AM
Originally Posted By GHPorter:
Originally Posted By jws360:
Almost glad to see I am not the only one confused. Just to make 100% sure, the correct figure is FOOT-POUNDS, correct?

Maybe someone with more authority here can make this part of a sticky so as to correct an apparently longstanding issue.


Nope, it's the other way around. A carbine (adjustable stock) tube's lock nut (castle nut) is torqued to 40±2 INCH POUNDS. Using the other units on the castle nut could strip the tube out of the back of the lower, ruining the lower.



Did you read the Colt manual I posted the link to?
Does the barrel nut strip off the receiver when you torque it to 80 foot pounds?
nicholsmf  [Team Member]
12/22/2008 7:03:46 AM
TM9-1005-319-23

Page 200


j3_  [Team Member]
12/22/2008 7:08:13 AM
Read the link to the Colt manual value for the nut. Look at the value for a standard receiver extensions.
40 inch pounds is what a simple 8/32 screw can be torqued to.

Does anyone even have the wrench that is supposed to be used on the nut anyway. Does anyone even sell one that is made for a torque wrench?
OrangeLazarus  [Member]
12/22/2008 8:38:48 AM
My manual says use a buttstock spanner and tighten with a good "HMMMF". I don't use a torque wrench for my barrels and I'm sure as hell not going to use one for a castle nut.....

Seriously, 40 inch-pounds converts to only 3 foot-pounds. Seems like kind of a light amount of force to me.
jws360  [Member]
12/22/2008 8:53:18 AM
Originally Posted By GHPorter:
Originally Posted By jws360:
Almost glad to see I am not the only one confused. Just to make 100% sure, the correct figure is FOOT-POUNDS, correct?

Maybe someone with more authority here can make this part of a sticky so as to correct an apparently longstanding issue.


Nope, it's the other way around. A carbine (adjustable stock) tube's lock nut (castle nut) is torqued to 40±2 INCH POUNDS. Using the other units on the castle nut could strip the tube out of the back of the lower, ruining the lower.


This is odd- The Cnadian manual specifically says FOOT lbs as does Brownell's "How to assemble an AR-15" video. I've found a few sites that claim the "inch lbs" in this edition of the Colt manual is a typo.

Perhaps we need a definitive answer.
tracecom  [Team Member]
12/22/2008 9:16:07 AM
OK, there is another issue in the TM9-1005-319-23, Page 200 excerpt. Step 6.B. says to place the castle nut with the three notches facing forward. Assuming that means toward the muzzle, I looked at the one I put on yesterday and saw that I had the notches toward the butt and started to take it apart. Then I decided to look at my factory built Bushmaster; it had the notches on the castle nut facing the butt.

Maybe the TM9-1005-319-23 is like a lot of publications: full of errors?

ETA: On closer inspection of the castle nut, I see it has three notches on both sides: small notches on one side and larger notches on the other. So I guess that either way I put it on, there are three notches are facing the front and the rear.

Having started my career as a technical writer, I know they make mistakes - usually because an engineer gives them wrong information.
GHPorter  [Team Member]
12/22/2008 11:23:30 AM
Originally Posted By jws360:
Originally Posted By GHPorter:
Originally Posted By jws360:
Almost glad to see I am not the only one confused. Just to make 100% sure, the correct figure is FOOT-POUNDS, correct?

Maybe someone with more authority here can make this part of a sticky so as to correct an apparently longstanding issue.


Nope, it's the other way around. A carbine (adjustable stock) tube's lock nut (castle nut) is torqued to 40±2 INCH POUNDS. Using the other units on the castle nut could strip the tube out of the back of the lower, ruining the lower.


This is odd- The Cnadian manual specifically says FOOT lbs as does Brownell's "How to assemble an AR-15" video. I've found a few sites that claim the "inch lbs" in this edition of the Colt manual is a typo.

Perhaps we need a definitive answer.
Don't confuse the RIFLE buffer tube and its torque requirement with the CARBINE buffer tube lock nut and its torque requirement.

j3_  [Team Member]
12/22/2008 11:32:17 AM
Originally Posted By GHPorter:
Originally Posted By jws360:
Originally Posted By GHPorter:
Originally Posted By jws360:
Almost glad to see I am not the only one confused. Just to make 100% sure, the correct figure is FOOT-POUNDS, correct?

Maybe someone with more authority here can make this part of a sticky so as to correct an apparently longstanding issue.


Nope, it's the other way around. A carbine (adjustable stock) tube's lock nut (castle nut) is torqued to 40±2 INCH POUNDS. Using the other units on the castle nut could strip the tube out of the back of the lower, ruining the lower.


This is odd- The Cnadian manual specifically says FOOT lbs as does Brownell's "How to assemble an AR-15" video. I've found a few sites that claim the "inch lbs" in this edition of the Colt manual is a typo.

Perhaps we need a definitive answer.
Don't confuse the RIFLE buffer tube and its torque requirement with the CARBINE buffer tube lock nut and its torque requirement.


No confusion. You have not read the Colt manual on the link have you?



Take a chance Columbus did.
puskrat  [Life Member]
12/22/2008 11:38:01 AM
Originally Posted By j3_:
Originally Posted By puskrat:
Technical Manual
35-39 lb ft. When tool and torque wrench used together.

page 199

Also, I have installed three stocks, never measured the torque.


That manual is where the confusion comes from as it list the nut as inch pounds.


http://www.coltcanada.com/techpubs.htm
this is alink to the Colt manual. Page 3-2-41 an 42 of the maintenance manual list it as foot pounds.


YIKES!!! I misquoted my own source. I quoted the rifle spec. I'll just be over here stickbeating myself––––––––––––>
GHPorter  [Team Member]
12/22/2008 11:58:45 AM
Originally Posted By j3_:
No confusion. You have not read the Colt manual on the link have you?
Yes I did, and it looks like a typo in that manual. Interesting that both the rifle buffer tube and the carbine tube lock nut have the same torque spec there (pages 3-2-39 and 3-2-42 respectively), but not in other manuals. The -23 has been updated, corrected, edited and otherwise reviewed many, many times. It says on page 3-81.1 (change 3) that the carbine tube lock nut is torqued to 40±2 inch pounds, while on page 3-81 (also change 3) the rifle buffer tube is torqued into the lower with 35-39 foot pounds of torque. I tend to believe the -23, which has been reviewed by many, many people over the apparently closely held Colt Canada manual.
jmorg51  [Team Member]
12/22/2008 2:12:16 PM
OK, who has a castle nut wrench with a cut-out for the torque wrench. After stripping out bolts in aluminum over the years in auto and marine applications, I like to measure these. Iron/steel I'm not to worried about. I don't have a buffer sized Heli-Coil set.
hellbound  [Team Member]
12/22/2008 2:18:26 PM
it doesn't really matter if you stake the castle nut like you're supposed to...
j3_  [Team Member]
12/22/2008 3:55:18 PM
I believe the Colt manual is correct. To much difference in the two measurements. Both tubes are aluminum threaded into the same material.
jws360  [Member]
12/22/2008 5:59:47 PM
Originally Posted By jmorg51:
OK, who has a castle nut wrench with a cut-out for the torque wrench. After stripping out bolts in aluminum over the years in auto and marine applications, I like to measure these. Iron/steel I'm not to worried about. I don't have a buffer sized Heli-Coil set.


EXACTLY––- I've stripped a few fasteners restoring some old Suzuki enduros and am quite concerned, which is why I religiously follow torque values.

I just can't see it being 40 inch-lbs. Many small screws use more than that!

Besides, what about the Canadian manual which says FOOT LBS and Brownell's video (link below) which also says FOOTlbs?

Brownells link that says FOOT lbs: http://www.brownells.com/aspx/NS/GunTech/NewsletterArchive.aspx?x=v&p=0&t=1&i=939
j3_  [Team Member]
12/22/2008 7:33:42 PM
I am not sure I would try to torque a commercial tube to that higher value. On some of them I have had the major diameter of the threads was less than that of a mil. sized tubes thread.
A rifle tube torque to the forty pound is a pain to remove.
Guess I will buy one of the Brownells wrench next month just to see how it feels when you torque one to that value. I doubt I have ever came close to that value with the hand wrench I have.
RSM  [Team Member]
12/22/2008 11:16:51 PM
Good grief folks.

First consider that the US Govt. can't even write a decent spec for an air conditioner without dozens of errors.

Then use common sense. 3-1/2 ft/lbs would be light for a 6mm bolt threaded into aluminum. Look at the size of those threads!

Granted- 40 ft/lbs is probably excessive but it isn't gonna rip the threads out. (Although I am also suspicious of the undersized commercial threads.)

I have never used that much however, for fear of flexing the receiver .

Fall back on common sense and the "hmmf" comment. (I think that was a Kuleck quote?)


BTW- The OD of commercial threads varies quite a bit with manufacturer.
AKM  [Member]
12/23/2008 9:17:58 AM
Use common sense guys.

Do you believe the rear extension/castle nut could survive as much or more torque then the barrel nut? I think not.

Do you believe that those stamped sheet metal castle nut wrenches could survive as much torque as a barrel nut wrench? I think not.

tamu94  [Team Member]
12/23/2008 10:11:47 AM
Speaking from experience, you can strip the threads by overtorquing.

The castle nut itself will not strip them (unless you REALLY try) but the key will slip out of the key way and over the threads from the excessive torque.

You will be left with with a slightly twisted stock in relation to the upper.

I was able to do this on my first stock replacement by using about 15 ft-lbs.

The spec is 40 in-lbs. Its all you need if you properly stake it.
skulpin  [Team Member]
12/23/2008 10:49:01 AM
+1 on the common sense. I can see where the confusion comes from. I have a Rock River stamped wrench and it has no facility for a 1/2" drive torgue wrench (carbine lock ring & fixed rifle extension utility only) whereas the Brownell's #080-216-017 (no longer sold) Carbine Spanner Wrench (tool head) instructions specifically state...

Quote:
"The Spanner Wrench should be used with a self-limiting, 1/2" drive torque wrench to turn the Nut in a clockwise direction. Note: The Lock Nut is to be torqued to between 38-42 foot pounds of pressure. DO NOT EXCEED 42 FOOT POUNDS OF PRESSURE! Excessive pressure may result in stripping the threads in the Lower Receiver. However, insufficient torque may not adequately secure the Receiver Extension."

The Brownells wrench head I have is ancient as well as the instruction sheet that came with it. I believe Brownells discontinued the one I have in favor of their 080-000-291AB & 080-216-015AB tools.

Somebody sure got the wires crossed on the torque spec's.
RSM  [Team Member]
12/23/2008 7:21:43 PM
Originally Posted By tamu94:

The spec is 40 in-lbs. Its all you need if you properly stake it.


Actually you need even less than you think......

You don't need a tool! I just tightened a large bolt to 40 inch/lbs. and then removed it with two fingers (no wrench) by hand without even straining!

I think catchup bottle lids are tightened to more than 40 inch/lbs and that's a glass bottle!

I don't think I'd trust my stock at that torque
Note: That's with the *full* 40 inch/lbs. applied to the fastener. If you assume you're using something like a CAR stock wrench with a square hole partway along it for the torque wrench drive your actual applied torque would be more like 30 inch/lbs. Something akin to the little screws that hold your computer together......
jws360  [Member]
12/23/2008 8:22:40 PM
I think I have an answer:

Sent a message to Ken at Sawlesales.com, who sells Colt parts. Here is his response:

There is a HUGE difference between a forged and an extruded rec extension. You are looking at fixed stock (rifle) rec extensions.
The extruded items are softer, much lower quality items. The kind of stuff you find on aftermarket-junk guns.

All torque values on the M16/M4 are in FT/LBS, except the screws which hold the key in place.

Yes, the rec extension nut should be correctly stakes, as designed. No, loctite is not an alternative.

Take Care,
Ken

Ken Elmore

Specialized Armament (1990 - Present)
Instructor, COLT Defense (1997 - 2007)
Sergeant, US Army (1986 - 1990)

j3_  [Team Member]
12/23/2008 9:06:57 PM
Originally Posted By jws360:
I think I have an answer:

Sent a message to Ken at Sawlesales.com, who sells Colt parts. Here is his response:

There is a HUGE difference between a forged and an extruded rec extension. You are looking at fixed stock (rifle) rec extensions.
The extruded items are softer, much lower quality items. The kind of stuff you find on aftermarket-junk guns.

All torque values on the M16/M4 are in FT/LBS, except the screws which hold the key in place.

Yes, the rec extension nut should be correctly stakes, as designed. No, loctite is not an alternative.

Take Care,
Ken

Ken Elmore

Specialized Armament (1990 - Present)
Instructor, COLT Defense (1997 - 2007)
Sergeant, US Army (1986 - 1990)



I am not sure why it took more than the link to the Colt manual but I am glad you found an answer you seem to be comfortable with.
jws360  [Member]
12/23/2008 9:36:48 PM
Originally Posted By j3_:

I am not sure why it took more than the link to the Colt manual but I am glad you found an answer you seem to be comfortable with.


I was confused since the original Colt manual said "inch lbs", which makes little sense and which appears to be a typo. Besides, the answer wasn't just for me––it was for everyone who wants to do things "right" and by the book. The way I see it, engineers designers specify certain figures & values for a reason.
556Cliff  [Member]
12/23/2008 10:01:12 PM
Originally Posted By jws360:
Originally Posted By j3_:

I am not sure why it took more than the link to the Colt manual but I am glad you found an answer you seem to be comfortable with.


I was confused since the original Colt manual said "inch lbs", which makes little sense and which appears to be a typo. Besides, the answer wasn't just for me––it was for everyone who wants to do things "right" and by the book. The way I see it, engineers designers specify certain figures & values for a reason.


Thanks!

I have looked for an answer for this nagging question for quite some time.

I've had threads about this in the past and never got as good of an answer as the one you got from Ken Elmore.


What was your question about rifle receiver extensions?
jws360  [Member]
12/23/2008 10:39:26 PM
Originally Posted By 556Cliff:

Thanks!

I have looked for an answer for this nagging question for quite some time.

I've had threads about this in the past and never got as good of an answer as the one you got from Ken Elmore.


What was your question about rifle receiver extensions?


I was curious as to the difference between forged & extruded buffer tubes. According to Ken's site, Sawlesales.com, there are two possible buffer tubes for an M4. One is extruded at $35 and the other is forged at $75. How a tube can be forged is not clear to me, but that is what is says...... He doesn't have any, so it's a moot point. I'll likely go with an LMT SOPMOD stock/tube, which they tell me is milspec.
j3_  [Team Member]
12/23/2008 10:43:21 PM
Originally Posted By jws360:
Originally Posted By j3_:

I am not sure why it took more than the link to the Colt manual but I am glad you found an answer you seem to be comfortable with.


I was confused since the original Colt manual said "inch lbs", which makes little sense and which appears to be a typo. Besides, the answer wasn't just for me––it was for everyone who wants to do things "right" and by the book. The way I see it, engineers designers specify certain figures & values for a reason.


The TM is not a Colt manual.
jws360  [Member]
12/23/2008 10:47:43 PM
Originally Posted By j3_:

The TM is not a Colt manual.


You are correct. I should have referenced the Technical Manual........

Oh, well... At least we have a definitive answer.
j3_  [Team Member]
12/23/2008 10:59:40 PM
Untill the question gets asked again in a week or two.
RSM  [Team Member]
12/24/2008 12:14:34 AM
Originally Posted By jws360:

One is extruded at $35 and the other is forged at $75. How a tube can be forged is not clear to me, but that is what is says...... He doesn't have any, so it's a moot point.


PK had Mil Spec (forged) buffer tubes for about $30-$35 last week. Midway sometimes has them for $30.

Bravo sells the mil-spec tube with a spring, buffer, plate and nut for $55.

RSM  [Team Member]
12/24/2008 12:21:27 AM
Originally Posted By jws360:
The kind of stuff you find on aftermarket-junk guns.



Looks like somebody forgot the first rule of sales. Sell on YOUR merits, don't go around spouting exaggerated nasty stuff about your competition. I guess BM, RRA, Armalite et al are just.....junk.....
RSM  [Team Member]
12/24/2008 12:28:20 AM
Originally Posted By jws360:
IYes, the rec extension nut should be correctly stakes, as designed. No, loctite is not an alternative.



IMHO- A good critical threaded joint uses Locking Compound to keep it from loosening and staking, peening or safety wire/clips to keep it from coming off. There is a significant difference between loosening and coming off. One of the most important reasons for staking is human error prevention not "loosening" prevention. QC can SEE a stake, they can't see loctite. Use both. Even good staking can still allow a degree of loosening as thread stretch relaxes.

Nate7out  [Team Member]
1/4/2009 4:49:42 PM
Originally Posted By tamu94:
Speaking from experience, you can strip the threads by overtorquing.

The castle nut itself will not strip them (unless you REALLY try) but the key will slip out of the key way and over the threads from the excessive torque.

You will be left with with a slightly twisted stock in relation to the upper.

I was able to do this on my first stock replacement by using about 15 ft-lbs.

The spec is 40 in-lbs. Its all you need if you properly stake it.


I just did a build and my stock is slightly twisted relative to the receiver. It is because the receiver extension threads are twisted onto the end plate key. I don't think I torqued it to 40 ft-lbs, I just snugged it up with the small wrench after hand tightening it.
jws360  [Member]
1/15/2009 9:04:46 PM
UPDATE: I got the following email from Bushmaster on the correct torque setting:


I purchased a collapsable stock assembly from you and have a question: What is the proper torque value for the nut? I prefer to be precise rather than risk damage or something coming loose. Also, so you have info on the proper techniques on staking the nut? I checked the website, but did not see anything. of course, I could be blind...... Thanks.

Answer / Solution

The locking nut should be torqued to 32 to 35 ft lbs. There are three notches in the locking ring that contact the adaptor plate. Two of the three notches can be staked using a drift punch ground down to a rectangular shape that fits the notches.


Direct Link to This FAQ

http://www.bushmaster.com/faqs/?f=904