How much torque on barrels

[Will Henry]

When I started fitting barrels, I was told to allow .002" for compression when cutting the chamber. So, if my measurement showed the bolt face to be .130" away from the face of the barrel, I would cut the chamber so the "go" gauge protruded .128". Generally speaking, this worked out fine but I doubt there is that much compression with a real good fit (a trued or custom action and a flat shoulder contact). Nonetheless, if you chamber a barrel with zero headspace, the bolt won't close on the gauge when the barrel is tightened on so there is some compression for sure. Barrels where the shoulder is undercut slightly, so the shoulder contacts on the outer edge first, will definitely deform at the shoulder enough to change the headspace. WH

 

[Eloudamy]

What about “hand tight” without a wrench?

I have a friend who is now in his 70’s and has competed all his adult life. I’ve seen him twist one barrel off by hand, literally, and screw another on for a different string of fire shooting varmint BR. He didn’t use a wrench, a vise, nothing. He says it doesn’t change accuracy and is never a problem.

He’s a super-smart guy and when he speaks, to me it’s kinda like E.F. Hutton, I listen. He has always steered me right and has the experience to back it up.

With that said, this is baffling to me, that he might have 10 Ft-lbs torque at most, and there’s no change in accuracy.

also, with a RH twist, doesn’t the barrel also try to tighten itself as you shoot?

 

[DaveTooley]

I've had barrels shoot loose in competition. It will have you pulling your hair out trying to figure out what's wrong.

 

[Will Henry]

Yes. A friend was shooting in a Palma match when he suddenly started drifting left. He had noticed the front sight was canted a bit right so he just grabbed the barrel in both hands, backed it off a bit, then snapped it in. It went a little past the witness mark and now, it was shooting a bit right but it stayed for the rest of the match. He had set the barrel back just prior to the match and had gone a little far so the barrel was not real tight. He torqued it up and re-set the sight afterward. WH

 

[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.

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.

I found some additional information about this. That information states that they torque their barrels to 500 Ft Lbs.

 

[Dusty Stevens]

I found some additional information about this. That information states that they torque their barrels to 500 Ft Lbs.

That is rediculous. I wonder if he actually has a torque wrench?

 

[carlsbad]

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.

Grimstod,
I think you should check your math. Here is what I calculate.

1. Assume 40KSI yield strength for 416. It is probably higher in the hardened state but 40ksi is a good conservative number.
2. 1.060 threads. Effective diameter at the root of 1". this yields area at root of .785 sq in.
3. Nut factor K=.2 like you.
4. Chamber is .486 diameter. I think that is what you used. area of chamber is .185 sq in.
5. Stress area is .785-.185 = .6 sq in.

So yield would be .6 x 40,000 = 24,000lbs.

Plugging into T=.2Fd I get 424 ft lbs for yield. This is conservative.

So I've always considered yield of the tenon irrelevant and in fact, at the torques we are applying we are not going to get significant stretch. This is good and bad. No stretch means the chamber will stay as we cut it. Bad because we don't have the stretch to ensure preload is applied during firing. But we know that a well cut thread will stay tight with low torque. I believe this more from experience than from engineering. If this were a joint in a power plant, I'd use 200-225 ft lbs (half of yield). In a precision instrument (rifle) I try to minimize excessive stresses and I've started using 40 to 50 ft lbs with good success.

--erry

 

[butchlambert]

I found some additional information about this. That information states that they torque their barrels to 500 Ft Lbs.

I'll call bull shift on 500 ft lbs.

 

[Ggmac]

That is rediculous. I wonder if he actually has a torque wrench?

Maybe a 1” pneumatic gun

 

[ebb]

So after 8 pages of this thread I have learned that when i torque a barrel it should be between 40 and 500 foot lbs.

 

[Edd]

So after 8 pages of this thread I have learned that when i torque a barrel it should be between 40 and 500 foot lbs.

That should be an easy target to hit.

 

[carlsbad]

So after 8 pages of this thread I have learned that when i torque a barrel it should be between 40 and 500 foot lbs.

This thread points out the importance of being able to sort the wheat from the chaff on the internet.

 

[carlsbad]

I'll call bull shift on 500 ft lbs.

Fully agree. the threads would take it but most actions would be damaged.

 

[Edd]

Fully agree. the threads would take it but most actions would be damaged.

What part of the actions would be damaged?

 

[carlsbad]

What part of the actions would be damaged?

Depends what wrench you use on it. internal wrenches would twist and likey fail and twist the action at the weak points where the ejection port is. External wrench would likely slip and scar the exterior.

 

[Dusty Stevens]

Kelbly installs their stainless thread inserts into the panda with either 250 or 350 lbft of torque

 

[Curmudgeon]

50 to 55 ft pounds, because of variance, on a flush barrel and receiver. Don’t forget the thread lube.

 

[Dgd6mm]

40-45 ft. lbs. works for me.

This works for me.

 

[jelenko]

Is it OK to use anti seize - assuming the torque is 40-50 ft lbs?

 

[Dgd6mm]

Is it OK to use anti seize - assuming the torque is 40-50 ft lbs?

Yes definitely.