Switch Barrel Torque

Jec

Without being too rude, I will say that you are getting some bad advice from some shooters who seem to be ignorant of this entire concept of how threaded joints work.

The link over to Sniper Hide isn't much better.......jackie
 
Last edited:
Thankyou gentlemen. After all was said, I have decided that for my application, I will apply anti-galling compound / make an index mark at the "snug up" position/ torque to 110 ft.lbs / measure the index mark travel to insure I have at least 1/8" travel. I will set 3/32 as my target, and adjust torque to that target.
I'd like to thank everybody who provided input! Having several points of view to evaluate prompts research and has certainly given me a better understanding of switch barrel principles. Hopefully, a year from now, I will have enough experience to offer an opinion when another "rookie" asks the same question.
 
Barrel torque

I just headspaced a Savage, with the barrel nut, and after running it up hand tight I was able to turn the nut about 1/4 turn with the spanner wrench. I didn't take the time (I was in a hurry) to put a torque wrench on the spanner wrench (with computed offset), but I would guess I was under 100 lbs. torque. I had applied anti-sieze to the barrel threads so that both the barrel nut and the action threads were riding on the anti-sieze. That is a good system for headspacing, but requires removing the action from the stock and scope from the rifle to switch barrels. On-line recommendations seem to be anywhere from 20-70 lbs. for the Savage.
 
I'm building my first switchbarrel now. I guess I have an overly-simplistic view of torque - my plan is to start at some small figure, fire a string, snug it up some more, fire, etc. until further tightening shows no change.

Why guess when you can collect your own data?
 
Savage barrel nut torque

The Wheeler Engineering barrel nut wrench comes with instructions to torque the barrel nut to 30-40 Ft.-Lbs. I didn't use my torque wrench, but I'm sure I went past that.

If you look at the attached picture you will see there is either a 1.5" or 8.0" offset from the center of the nut. If you set the torque wrench for 30 or 40 Ft.-Lbs. and you calculate that extension as 1.5" you get a 10% increase in torque or 33-44 Ft.-Lbs. If you used the drive hole at 8.0" the torque would increase 50% and would be 45-60 Ft.-Lbs. If you actually want 30 or 40 Ft.-Lbs. on the nut you would decrease the torque 10% for the 1.5" extension (27-37) and 33% for the 8.0" extension (20-27).

A lot of experience and a lot of variables that could affect torque have been brought out in this forum. There is also a good article in the May 2009 issue of Precision Shooting, "Proper Barrel Tightening Torque" by James A. Boatright. Two points he brings out are that torque won't overcome poor alignment and that too much torque on V threads can cause chamber distortion that could give a false headspace reading.
 

Attachments

  • spanner and torque wrench.jpg
    spanner and torque wrench.jpg
    24.2 KB · Views: 327
Here's another thing to think about for all you loose barrel shooters.

Bolt thrust.

If there is "bolt thrust" then we must consider that "thrust" works both ways. The thrust that's pushing BACK on the bolt is also pushing FORWARD on the barrel. I think that perty much everyone can visualize that if we jammed a screwdriver into the gap between the boltface and the barrel we could wedge it open..... and with it wedged open we'd open a gap at the shoulder that abuts the action...... it then becomes easy to see that with a gap showing there's nothing to keep the barrel from rocking on the threads.


In real life the bolt thrust DOES wedge the barrel forward unlocking this shoulder, and it DOES come back to rest in a different spot and groups DO move around.


altho some guys don't shoot well enough to see it.



al
 
Thanks, Al

You've just given me an explanation that I can understand, of how a barrel could loosen.
Thanks, Ron
 
I just don't know if it's me or my loose barrel :)
 

Attachments

  • 6mm BR 5 shot.jpg
    6mm BR 5 shot.jpg
    29.9 KB · Views: 397
Verticle

That type of verticle is usually a indication that you need to go up a little on the powder for what ever load window you are in.

Looks like N133 on a 75 degree day at 20 percent humidity.............jackie
 
Not that it matters much

BUT, after reading this and the discussion I had with a friend who is an Engineer the other day, the Witness Marks make the most sense. This leads to a question:

1. How does one estalish the distance witness marks should be apart?

This is not to discredit the 3/32 but say for a different diamater barrel like a .22RF , etc. I am betting there is a formula :).
 
RE: Me or loose barrel

Thanks for your input :)

I'm a varmint hunter, not a benchrest shooter, and I shoot off a bipod. I'm happy with my rifle which is a blue-printed Remington 700 with an Adams & Bennet button-rifled barrel, chambered between centers, and bedded in a Bell & Carslon Duramax stock. The chamber is a .272 no-turn neck. The bullet is a 87 gr V-Max and the powder is W748 (can't afford Vihtavuori). I was playing the devil's advocate, it's good enough for me.

One comment posted here and I've seen in print is that the bullet will torque the barrel, so I'm assuming that refers to a RH twist since actions are RH thread. Would a LH twist unthread a barrel?

My resources are limited, but I may try (if no one beats me to it) is headspacing a barrel with no shoulder on a Savage action without the nut and making a reference mark and see if 1) closing the bolt rotates the barrel, and then 2) if the barrel moves when fired and how much, or how many rounds it takes to move, and 3) if I can fire 3 or more rounds before it moves, what kind of group I get.

You can tell I have too much time on my hands (and not enough money) - nhk
 
As far as I can tell, what is at stake here is accuracy, not safety.

From a benchrest -- or high accuracy -- perspective, the reason we need the barrel secure is the aiming system -- the scope -- is mounted on the receiver. If the barrel can move, even slightly or occasionally, when it does so, the bullet will not go were the crosshairs point. It is as simple as that.
 
Savage barrel nut torque

nhkuehl said:
I just headspaced a Savage, with the barrel nut, and after running it up hand tight I was able to turn the nut about 1/4 turn with the spanner wrench. I didn't take the time (I was in a hurry) to put a torque wrench on the spanner wrench (with computed offset), but I would guess I was under 100 lbs. torque. I had applied anti-sieze to the barrel threads so that both the barrel nut and the action threads were riding on the anti-sieze. That is a good system for headspacing, but requires removing the action from the stock and scope from the rifle to switch barrels. On-line recommendations seem to be anywhere from 20-70 lbs. for the Savage.
Click to expand...

After searching for the correct torque to use on the Savage barrel nut, I ran across an article in the August 24th, 2006 article in Machine Design entitled 'Keeping firearms on Target'. (ref. machine design.com:keeping firearms on target). The article was about Savage Arms with input from Ron Coburn, CEO.

On page two of the article is a picture with a caption describing the tightening of the locknut on a Savage; the following is a direct quote from that article. "He is using an extension bar with a built-in torque wrench that lets go at 70 ft-lb". Note this value is for a Savage nut not a Remington. I have noticed that torquing the barrel nut to the proper torque definitely improved group size. For my Remington actions, I have a Kelbly rear action wrench that I'm going to modify so that I can use a torque wrench. Up until reading this thread I've been snugging my barrels by feel.

One comment on torque wrenches. Unless a torque wrench is periodically calibrated, the torque could be under or over the amount required. Dropping a wrench or banging it could significantly alter the reading.

Lou Baccino
 
I noticed

on a rifle I was handeling the other day the Smith or Owner had struck a mark on the action and one on barrel as a location point for re-assembly. This seems to me to be a good practice once one finds the correct location.
 
Pete Wass said:
on a rifle I was handeling the other day the Smith or Owner had struck a mark on the action and one on barrel as a location point for re-assembly. This seems to me to be a good practice once one finds the correct location.
Click to expand...

I see alignment marks on the barrel shoulder and bottom of receiver on military Mausers and 91/30 Mosin Nagants.
 
witness marks

I put a .22 rf barrel on a custom action , the threads I cut were between a class 2 and class 3 fit. I snugged by hand the barrel to action and then put a witness mark on them. TIGHTENED with action wrench. The witness marks moved 9/64. I didn't try it with a tork wrench but was able to repeat the same 9/64 over again . This was a SS action and barrel with anti seize on it. I felt like I had loaded the threads pretty good.
 
Last edited:
Hand tight

I guess 'hand tight' would be arbitrary, since that would very from person to person. nhk
 
9/32!!!!!!!!!!!

When I take a typical 1.062 diameter 16 tpi, and advance the witness marks, (from firmly seated), 3/32, that takes 120 ft lbs. Are you sure about that 9/32........jackie
 
You must log in or register to reply here.
Back
Top