How much torque on barrels

[Raythemanroe]

I see some actions that look stout enough to take 200-500# of force without a little warpage.. I wouldn't be paying anyone to find out what they can take.


Ray

 

[scooter]

I had Larry Racine build a switch barrel gun for me with his quick change system (the one with the hex on the muzzle) and tighten it up with a box wrench snugged up, and then give it a whack with another box wrench, but not too hard. Using these instructions seem to work good for me.

 

[Grimstod]

I was wondering if this would get brought back up. :


So I did do lots of research on this and one member here who is a physics/mechanics engineer. Showed me the formulas and after a few tries at it and a hole evening typing stuff into calculators I cam up with 62 lbs for the MNagant.

Here is how I have come to my conclusion. I had the same engineer look over all the numbers and he said they check out ok.

Area of barrel threads(tenon)
0.785*(.975-1.0825*.0625)^2=0.507

Area of chamber
0.507 [3.14 * .0.486^2 / 4] = 0.3214 sq in

Yield of metal used
20,000* .3214= 6428 lbf

T= .2FD. the .2 is the Nut factor which depends
on lubricant and thread quality. .2 is most often used for common bolt
threads without lubricant. for high quality lathe cut gun threads with
lubricant, you should probably use .10 to .15. I'll use .12
0.12*6428*0.975/12= 62.6lbs


In conclusion this is the max number you would want to torque to without doing any permanent damage. In reality you could probably go much lower as other smiths here have 40 pounds and I like that number and will use it in the future.

 

[Barlow]

Interesting thread (pun intended). I have a question. Do you switch barrel guys use witness marks? I have a Marlin X7 that was a 308 that I put a 6 Dasher barrel on, that I may switch back and forth. I haven't done it yet cause I'm having too much fun with the Dasher, but will switch them in the future. Thanks Barlow

 

[butchlambert]

No, but if you want to? I have been switching barrels for years. Haven't heared positive info on HS change.

 

[Minesweeper3433]

On the subject of anti seize on barrel threads. US Army TM for the M16/M4 series rifles dictates a very similar process to what was listed earlier in this thread regarding tightening and loosening the barrel nut multiple times before final torque to spec and alignment. As well as anti seize being used throughout the process and for final assembly. Although I think this may have more to do with a steel nut on aluminum threads I would enjoy reading the research they had to have done at some point to come to that process. Myself I use anti seize on the threads of my rifles and tighten by hand only by quickly spinning the action onto the barrel with small action wrench while the barrel is held in barrel vise. I have gone back and broken these barrels loose with a strap wrench at the range when I had a stuck case in the chamber and was very glad I could do that at the time. Untill I learn of a reason to torque a barrel on a bolt action over "snug" I don't think I'll waiste the energy forcing anything.

 

[spclark]

High quality threads don't need 'excessive' torque to stay tight.

The disparate metals situation with steel on aluminum makes the tighten / loosen / tighten thing necessary because the aluminum will "move" a little with each cycle. You're literally "work-hardening" the aluminum with this procedure until the aluminum ceases to move much, then you can count on the joint staying tight after the final torquing.

Anti-sieze is used to reduce friction & galling of the thread surfaces, making a predictable torque possible rather than a number adversely affected by an uncontrolled friction component.

Older, coarser metalwork requires a different approach, demanding more "oomph" to remain tight over use because of the nature of the metalwork involved. Add variables like age & potential corrosion, the situation grows even more complicated.

 

[fguffey]

Torque: It is assumed when torqueing two pieces together the two pieces get closer with 'more torque', not true. Excessive torque pulls threads, create stress and galls the mating surfaces. I have old action wrenches that do not have a handle, a 48" pipe wrench will fit them but they were designed to be used with a hammer.

F. Guffey

 

[dakotaman]

I'm always seeking ways to make a long range precision rifle more precise and I have much respect for members of this site. A lot of tricks go into a precision build and barrel torque comes up often. Although I'm a scientist at heart, I seem to have arrived at my torque values from interviewing gunsmiths and shooters who have won 1000 yard national championships and from the experiences of my competition rifle's shooters. I've also studied the memoirs of precision rifle builders since the 1970s and queried receiver makers for their recommendations. Of all the various information I've considered , 40-50 ft/lbs is the most commonly used answer and I usually torque at 40 ft/lbs unless there is a reason why not (e.g. customer specification).

I like the idea mentioned here of cycling the threads back and forth to torque and will try that on my next build. It will become part of my build process if it reduces group size or F-Class scores. My suspicion is that its intrinsic value is far below the weakest link in the precision chain but I don't believe it can hurt so I'll try it. I really like the idea of locking those threads together perfectly and it might just help 100 yard groups get into those lower .0s.

Last week I did a build on my first Pierce Tungsten receiver and called them for their recommendation. I was concerned about galling with a stainless R-416 barrel torqued in the tungsten receiver with 18 TPI. They recommended 70 ft/lbs of torque with copper-based anti-seize and that is exactly what I will use for this build. I suspect that 40 ft/lbs will likely deliver identical precision but 70 is still quite reasonable to me so I'll use it.

Aside from that, it has been my experience that if a barrel rotates 1/8 turn after shoulder contact, the barrel is turning in the barrel vice. I detect very little if any barrel rotation when I hit 40 ft/lbs of torque. It may be compressing the threads internally a bit but not much.

 

[MatthewsCarbineCo]

He is not a gunsmith in any form of the definition... He is someone thinking he is. Tell him it is not like tightening a lug nut on a BUD wheel

 

[Tommie]

 

[Gappmast]

Do you guys think turning a barrel 1/8 - 1/4 turn past stop is stressing the threads and receiver?

It's been my experience with a good finish on the shoulder of the barrel and action when it stops it stops. I torque at 70LB for center fire and the amount of turn from stop to 70 LB is about zero.

 

[butchlambert]

I'm always seeking ways to make a long range precision rifle more precise and I have much respect for members of this site. A lot of tricks go into a precision build and barrel torque comes up often. Although I'm a scientist at heart, I seem to have arrived at my torque values from interviewing gunsmiths and shooters who have won 1000 yard national championships and from the experiences of my competition rifle's shooters. I've also studied the memoirs of precision rifle builders since the 1970s and queried receiver makers for their recommendations. Of all the various information I've considered , 40-50 ft/lbs is the most commonly used answer and I usually torque at 40 ft/lbs unless there is a reason why not (e.g. customer specification).

I like the idea mentioned here of cycling the threads back and forth to torque and will try that on my next build. It will become part of my build process if it reduces group size or F-Class scores. My suspicion is that its intrinsic value is far below the weakest link in the precision chain but I don't believe it can hurt so I'll try it. I really like the idea of locking those threads together perfectly and it might just help 100 yard groups get into those lower .0s.

Last week I did a build on my first Pierce Tungsten receiver and called them for their recommendation. I was concerned about galling with a stainless R-416 barrel torqued in the tungsten receiver with 18 TPI. They recommended 70 ft/lbs of torque with copper-based anti-seize and that is exactly what I will use for this build. I suspect that 40 ft/lbs will likely deliver identical precision but 70 is still quite reasonable to me so I'll use it.

Aside from that, it has been my experience that if a barrel rotates 1/8 turn after shoulder contact, the barrel is turning in the barrel vice. I detect very little if any barrel rotation when I hit 40 ft/lbs of torque. It may be compressing the threads internally a bit but not much.

When did John come out with a tungsten receiver? I have 2 rifles built with John's receivers, one in CM and the other is Ti.

 

[Edd]

On another website, I read a comment by Mike from Tac Ops that one of the things they do to maintain consistency in cold bore shots is "extreme high torque" on the receiver to barrel fit.

 

[Dusty Stevens]

When did John come out with a tungsten receiver? I have 2 rifles built with John's receivers, one in CM and the other is Ti.

Its for mountain rifles- less recoil than those pesky featherweights

 

[Shrek]

On another website, I read a comment by Mike from Tac Ops that one of the things they do to maintain consistency in cold bore shots is "extreme high torque" on the receiver to barrel fit.

Either Mike’s definition of extreme high torque is 40-70 pounds or he’s doing garbage machine work and parts and trying to compensate for the extreme low quality of the machine work. If 40-70 pounds won’t keep the barrel to action joint from moving its too sloppy. Undersized tennon or out of alignment action face to threaded joint. The more I learn the more I understand that there’s a lot of quaks in the shooting industry selling snake oil to ignorant buyers. I have no idea who Mike at Tac Ops is but the buzzword name sounds alarm bells to me and tells me all I need to know.

 

[Edd]

Either Mike’s definition of extreme high torque is 40-70 pounds or he’s doing garbage machine work and parts and trying to compensate for the extreme low quality of the machine work. If 40-70 pounds won’t keep the barrel to action joint from moving its too sloppy. Undersized tennon or out of alignment action face to threaded joint. The more I learn the more I understand that there’s a lot of quaks in the shooting industry selling snake oil to ignorant buyers. I have no idea who Mike at Tac Ops is but the buzzword name sounds alarm bells to me and tells me all I need to know.

He didn't give a number but I don't think 40-70 pounds would be his definition of extreme.

 

[carlsbad]

If he's an old guy with an 8' cheater to make it easier maybe he isn't over stressing anything.

Will 1/8 turn past stop cause a problem? depends on thread fit. If the thread fit is good, then 1/8 turn of 16 tpi thread has to find .008" of movement in the joint. that is a lot. Now if he makes crappy thread he may need close to .008 just to get the slop out of the threads.

--Jerry

 

[atblis]

snip...

Aside from that, it has been my experience that if a barrel rotates 1/8 turn after shoulder contact, the barrel is turning in the barrel vice. I detect very little if any barrel rotation when I hit 40 ft/lbs of torque. It may be compressing the threads internally a bit but not much.

Put a witness mark before torquing. Pencil works fine. Last R700 barrel I might have gotten 1/64 of a turn more before the barrel started slipping. Was aiming for 50 ft lbs. Headspace did tighten a slight amount (guessing 0.001"). Just another anecdote for the file...

 

[Aceball]

Pull tell your eyes bug out! Wait, that's the procedure for the Barrel Vise. Proper torque depends on type of receiver and the intended shooting application. I don't torque rimfire threads nearly as tight as sniper barrels. I actually go by feel on most of custom guns. You can tell to what degree, just close one eye. A 4 ft. Cheater Bar is damaging. Once over torqued the threads will never maintain proper engagement or grip. I Witness Mark my customers BR rifles with instructions never turn past the marks. About 40 to 60 lbs (except working guns) works for me with clean Brass Brushed threads coated with Tiger Milk or Moo Juice.

Harold Vaughn's book "Rifle Accuracy Facts" points out this dilemma in some detail.