Head Space and Barrel Torque

[Cort]

If a barrel is installed with proper head space at 70 foot pounds of torque, will it still have proper head space if it is removed and re-installed with 25 foot pounds of torque (or some other, lighter torque value)?

Cort

 

[Dusty Stevens]

Maybe. Its all in the thread stretch. But id bet itll be loose on headspace maybe by only .001

 

[carlsbad]

Shouldn't change much at all. The formula is T=.2Fd D is in feet for ft-lbs of torque. So using 1 1/16" diameter, Forces for 25 ft lbs and 70 ft lbs are 1400lbf and 5400 lbf respectively.

Assuming the outside of a 308 cartridge is about .460 effective diameter and the undercut diameter of the Remington tenon is .960 this give you the area of the steel of about .56 in2. So the stress on the area from the 3000 lbs difference is about 5400 psi. That's not much for quality steel.

Assuming youngs modulus E=30,000,000 psi which is normal for 416 and a lot of other steels, and with some other assumptions, I calculate the stretch to be about .00016" Negligible.

So the only change in headspace would be if you have some poor surface finish on either side of the recoil lug and the extra 3000lbf results in compressing some burrs.

--Jerry

 

[Dusty Stevens]

Damn jerry. You go boy. I only do that kinda stuff at work! Nice job

 

[carlsbad]

Thanks. I've done so many fastener calcs over 30+ years in a power plant that I don't really need much reference material any more. I do enjoy fully understanding threaded connections.

--Jerry

 

[Dusty Stevens]

Sounds like you do what i did up til a few months ago

 

[jdh47]

Have either of you guys read what Harold Vaughn wrote about threads in his book "Rifle Accuracy Facts"? Just wondering what you think about his comments on threads contributing to inaccuracy. He suggested rethinking the whole idea of barrel attachment. I'm not sure I'd go that far but it is interesting.

Joe

 

[carlsbad]

No I haven't. Hard book to come by. --Jerry

 

[clowdis]

No I haven't. Hard book to come by. --Jerry

Not hard to come by, just hard to justify the price!!!!!!!
http://www.amazon.com/Rifle-Accuracy-Facts-Harold-Vaughn/dp/1931220077

 

[butchlambert]

Wow!! I might need to sell my autographed copy!

 

[fguffey]

Wow!! I might need to sell my autographed copy!

Butchlambert, And I wonder just how much closer metal can get after it makes contact, then there is galling and thread pulling. Without anything between the barrel and receiver to crush I do not see the two pieces of metal closer.

F. Guffey

 

[savagedasher]

Remington style barrel the tighter it is torqued the less head space you will have. Savage the tighter it is Torqued the More head space you will have.. Larry

 

[carlsbad]

That's assuming a perfect fit. With a good surface finish and proper angles, it's a pretty good assumption. If the initial contact is dirty, has a burr, or poor angle causing a line contact, further torque can move it. --Jerry

Wow!! I might need to sell my autographed copy!

Butchlambert, And I wonder just how much closer metal can get after it makes contact, then there is galling and thread pulling. Without anything between the barrel and receiver to crush I do not see the two pieces of metal closer.

F. Guffey

 

[butchlambert]

Remington style barrel the tighter it is torqued the less head space you will have. Savage the tighter it is Torqued the More head space you will have.. Larry

And how does this happen? How will you torque a Remington type barrel enough to crush the shoulder or front ring?

 

[savagedasher]

Simple when you tighten a Remington type set up your the tighter you tighten the barrel every thing is going toward the bolt face..
Nut style ever thing is being pulled away from the bolt face. Savage when setting head space you can use a head space gauge that is tight and pull the clearance in that is need. Remington if the head space gauge is thigh it only get tighter with more Torque . Why do you think some Savage guns the nut is so tight?
Larry

 

[fguffey]

Why do you think some Savage guns the nut is so tight?

I do not know what Butchlambert thinks but for me I there is no procedure for setting the distance from the shoulder to the bolt face that calls for increasing the torque.

I do not have a head space gage that allows for a crush fit.

F. Guffey

 

[savagedasher]

Why do you think some Savage guns the nut is so tight?

I do not know what Butchlambert thinks but for me I there is no procedure for setting the distance from the shoulder to the bolt face that calls for increasing the torque.

I do not have a head space gage that allows for a crush fit.

F. Guffey

Your are correct As my first answer said. 70 FLB will have less head space then one with less. With a Savage their is no shoulder. Savage Not having a shoulder the lug ends up being the pressure area .
Action- lug - nut the barrel threads into the action. with lug being the pressure area when you tighten the
nut your are pulling the thread and barrel forward from the action. The tighter it tighten the more head space you will have. Larry

 

[Gundoktr]

I'll raise the bulschit flag on your original statement.

No change!

 

[fguffey]

No change!

I understand this is the forum that denies the luxury of disagreeing. So? At the risk of confusing members I will, I do not secure the lock ring to the die, I secure the die to the press with the lock ring, for the confused I will explain: I secure the die to the press by turning the lock nut while holding the die.

Holding the die and securing the lock ring removes the slack between the threads. Rotating the die changes the distance from the shoulder of the die to the deck of the shell holder. I understand, reloaders do not want to loose their place, at about this time someone will add the part about using an index.

It is a mechanical thing. The lock nut pushes on the front receiver ring, allowing the barrel to rotate at the same time the nut is secured is a bad habit.

F. Guffey

 

[savagedasher]

No change!

I understand this is the forum that denies the luxury of disagreeing. So? At the risk of confusing members I will, I do not secure the lock ring to the die, I secure the die to the press with the lock ring, for the confused I will explain: I secure the die to the press by turning the lock nut while holding the die.

Holding the die and securing the lock ring removes the slack between the threads. Rotating the die changes the distance from the shoulder of the die to the deck of the shell holder. I understand, reloaders do not want to loose their place, at about this time someone will add the part about using an index.

It is a mechanical thing. The lock nut pushes on the front receiver ring, allowing the barrel to rotate at the same time the nut is secured is a bad habit.

F. Guffey. When you tighten a nut their is no pushing it is all pulling the barrel away from the action the action and barrel both must be held while secure and not be allowed to move. Action wrench and barrel block is must Now you tightent the nut. All the clearance in the treads is being pulled forward The tighter the nut is the more head space you will get Larry