Barrel torque and effect on clearance ?

L

Lucky Shooter

Guest
A recent thread on barrel torque left no doubts as to the importance of tightening to torque ranges of 50 ft # to 100 ft # and above.

This raises the question to me as to how much these torque levels will affect clearances.

How much allowance above the desired clearance is necessary at these torque levels ?

Thanks.

A. Weldy
 
To get any measureable difference you would have to distort/compress the shoulder on the barrel. I've seen that once in 26 years of building rifles. That was on a factory Sako that wouldn't shoot.

Think about this. Depending on the diameter of the barrel, the location of the barrel vice, how hard would it be to twist the barrel when using these high torque numbers?

Dave
 
It has been my experience with measurements and fitting a new barrel and using a steel go gauge that I get about 2 thou "compression" on a gauge when the barrel is on tight. This is without distorting the shoulder... once fitted it can be removed and torqued tight again over and over and nothing changes. You can not tighten it so much that the shoulder would distort. Other damage would occur first.
 
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Quote from Jackie on barrel tightening

Quote:
"Torque is a subjective figure. There are factors that influence the amount ofload a nthread actually has in relation to the amount of torque applied. This includes the finish on then threads as well as the type of lubrication used.

I torque barrels to no less than 125 ft pounds. All you have to do is have a barrel that is not tight enough to ruin one week end match to know that it is better to have one a little too tight than too loose.

What I really do is go by the amount of radial advance of the barrel. I snug the barrel firmly, then place a magic marker spot on the barrel and the action, in line with each other. I then tighten the barrel to where there is about 3/32 movement between these two marks.

It just so happens it takes about 125 ft pounds on a 1.062 diameter 16 tpi to accomplish this." End quote.

Dave: I probably didn't word this as well as needed----concerning the question about the effect of torque on head space, bolt nose clearance and bolt lug clearance. Jackie refers to his radial advancement of about 3/32" past a "snug" witness mark. My concern was about how much this 3/32" radial advancement would advance the breech face closer to the bolt and if I need to allow for this advancement in the tenon dimensions if I want to guarantee a certain minimum clearance between the bolt and breech face.

Dennis: If I interpret your post correctly, you experience about .002" reduction in headspace when you tighten. Correct ?

Its not clear to me how the barrel torque affects the tenon dimensions and if allowances should be made.

A. Weldy
 
Dennis

On actions that have been trued I've never seen more than maybe a half thou change. What do account for the change you're seeing?

A. Weldy

Yes after you hand tighten or snap a barrel on the action it will rotate further around. That is nothing more than the threads of the action and the barrel distorting under the torque to fit each other. I still think there is no way we're going to compress the shoulder on the barrel unless there is very little bearing surface, then maybe.

I've check many barreled actions before and after tightening and see little difference in the headspace.

I torque barrels to about 80 ft/lbs. With lube

Dave
 
Dave Tooley said:
Dennis

On actions that have been trued I've never seen more than maybe a half thou change. What do account for the change you're seeing?


I torque barrels to about 80 ft/lbs. With lube

Dave
Click to expand...

Oops I have to agree with you, on custom actions and trued actions it is usually is less, but on the hundreds and hundreds of plain old factory rifles it usually is about 2 thou... I haven't really thought why it occurs I just think of it as compression for ease of measuring to get what I want...

I torque from about 100 pounds on up...
 
Lucky Shooter said:
Dennis: If I interpret your post correctly, you experience about .002" reduction in headspace when you tighten. Correct ?

Its not clear to me how the barrel torque affects the tenon dimensions and if allowances should be made.

A. Weldy
Click to expand...

Yes - if everything is done exactly to the measurements I find the headspace is about 2 thou too tight.

I attribute this to two different things... the fact that when measuring you do not apply the same force to the depth mic as the force that is applied when the barrel is torqued, plus the fact that steel is elastic and will compress slightly without distorting... so in effect the barrel tenon does screw into the action farther as the shoulder/action face compress.

Compression was not really explained when I was taught barrel fitting but it was mentioned that it would affect what you thought were correct measurements...
 
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Dennis

On plane jane factory acition I think the shoulders don't make full/even contact when screwed together until the final torque is applied. Then we are distorting the threads.

Dave
 
With factory barreled actions you would normally have a recoil lug. I could see how you would see more headspace reduction in this case especially if the lug is not ground. I'm with Dave, I have never noticed headspace being reduced enough to hardly detect on benchrest work.
 
Take a measurement from the face of the action to the bolt face.. for arguments sake lets say that measures .885".

Now chamber your barrel so the back of go the go gauge when in the chamber measures .885" to the shoulder of the barrel.

Now tighten that barrel on the action and try and close the bolt on that steel go gauge.

It won't close.

I'm joining Butch now.:)
 
With respect towards my elders, i have a question. This above statement got me to thinking...

. That is nothing more than the threads of the action and the barrel distorting under the torque to fit each other.
Click to expand...

I think i understand the thread pair sorta stretching out to fit each other and lock in tight. Don't throw rocks at me but if you tighten past this point would you ever reach a point where the bore would constrict maybe .0001 or .0003. If you keep tightening will the threads just pull apart and no constriction ever?

Maybe i'm just hungry but i keep seeing like "pulling taffy" before the threads pull... no? i ask because rimfire the threads 50/50 the lead. thanks joe:)

(should i just delete this outta my brain??)( i'm debateing wheather to push the submit reply button, i'm scared, lol)
 
There used to be a Calfee thread on this. Did you try the search?
 
Dave Tooley said:
To get any measureable difference you would have to distort/compress the shoulder on the barrel. I've seen that once in 26 years of building rifles. That was on a factory Sako that wouldn't shoot.

Think about this. Depending on the diameter of the barrel, the location of the barrel vice, how hard would it be to twist the barrel when using these high torque numbers?

Dave
Click to expand...


Dave, what do you think of the 1 1/8 tenons on inch two-fifty barrel shanks.... any issues?

thanks

al
 
Per how I look at it:

If there is an inner C ring, like on a Mauser, then that inner C ring does have some compliance.

If the breech touches the inner C ring while the shoulder and large ring are 0.0015" away from touching, then changes in torque can make up to 0.0015" in head space change.

Once the large ring and shoulder are in contact, the barrel can turn, but the force is just causing thread crush, and the change in head space is negligible.

With Mausers and barrels that the large ring and inner C ring get touched at the same point of barrel rotation, torque has little effect. I get the same accuracy from 5 foot pounds as 1000 foot pounds.
 
al

1 1/8" tenon would be on a custom action that we're paying big bucks for, assuming the threads are true. I have not seen any issues that could be traced back to the small contact area. How much contact is enough I don't know. I think that is as large as I would go on an 1 1/4 blank. I've got several rifles with that conditions. Getting ready to build a 338 Lapua Imp with a gain twist barrel, 1.250 blank and 1 1/8" tenon.


Dave
 
Dave,

There was that 1.350 barrel you put on my big BAT, which has a 1.250 tenon. I suppose there is a little more surface area with that set up, but the shoulder is smaller in the radial direction.

It shot rather well; a number of top-10s at the Nationals.
 
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