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Discussion in 'Gunsmithing' started by joe30007, Feb 15, 2010.
How much torque do you apply on installing a barrel?
100 ft LBs is usually as much as I ever give it, maybe 120 on mega calibres.
From 70 to 100 ft/lbs with just a little oil on the threads.
If you use an anti seize much less (50 to 70)
I like to use high pressure grease on the stainless threads to prevent Gaulding and
normally use 70 to 80 ft/lbs of torque.
I know some that use under 50 ft/lbs but have seen some shoot lose after heating up
and cooling down many times.
J E CUSTOM
Oh boy. OK, I confess, I use ~150 ft-lbs with antisieze on the threads and on the mating faces of the recoil lug and the barrel. The reason is to maintain tension in the joint in the face of differential thermal expansion between the barrel and the receiver. For those interested, the quantative explanation of differential thermal expansion (and other stresses on the threads and their effect on barrel stability) and what it does is in Rifle Accuracy Facts.
That's what I do, and why I do it.
True - it is in the book, but he was wrong on that. One should probably disregard that chapter. He said that low torque is bad for accuracy and that does not appear to hold up. He only tested it on one .270 rifle.
Here is some reading:
http://technology.calumet.purdue.edu/met/higley/PDF-Proper Barrel Tightening Torque.pdf
I, and many other BR shooters, have "hand snapped" barrels tight before a match and shot them all day with no ill effects.
125lbs with a synthetic grease that I bought to use on the ball links for my giant scale RC helicopter. (thankfully I came to my senses and sold that thing before throwing anymore visa cards at it!)
Eddie brings up a point. Please indulge another Chad Dixon longwinded dissertation.
Yes, many a BR guy swaps barrels the way formula one teams change tires. They crank them on hand tight and go for broke, shoot amazing groups, and it attempts to destroy all the little cardinal rules we've been taught since first building a rifle.
There's one thing you have to understand/realize though. It's apples and oranges.
I like apples btw.
Two terms to burn onto your hard drive: Group Size and Group Center.
A dedicated BR gun is a very specialized rifle that does one thing. The events are orchestrated so that a shooter can fire off just about as many sighters as he/she wishes. How this becomes relevant is that if you don't like the zero the gun has that particular day, go to the sighter target and start cranking knobs till you get what you want.
All they care about is group size.
Competitive (position shooting like highpower/palma, ect), tactical, varmint, hunting, rifles depend on both group center and group size. We want some assurances that the zero we establish today will be consistent the next time we pull the trigger. A hand tight barrel doesn't offer the assurances we need. Especially if the gun gets the snot shot out of it (like a highpower course gun, varmint rifle) because heat is going to be generated and things want to move around when they warm up. Especially barrel tennons.
To beat this horse a little more:
Hold your arm straight out, lock your elbow, and strain every muscle as hard as you can to hold it still. Now have someone try to move your arm. Doesn't take much effort for that person to steer you in whatever direction they want you to go. Now imagine all the forces at work on a barrel as that bullet is being accelerated from a dead stop to close to/over 2.5 times the speed of sound in a distance of just at/over two feet. You have linear acceleration and rotational acceleration along with crazy pressure, vibration, blah blah blah.
It's amazing these dumb things even hit the backstop!
All of that is managed by a threaded joint that's typically between 3/4"-1" in length and just over an inch in diameter. Amazing!
Thinking of it in these terms is why I habitually harp about the thread fit between barrel tennon/receiver being so very, very important. I try like hell to get mine to where they are just loose enough to not stick when assembling. It's a fine line and on rare occasion it does bite me (not so much anymore) and I end up buying the client a new barrel, but I truly believe the merits overshadow the risk.
Just my two cents on that.
Well said Chad.
Chad, I'll add two more cents, for a total of 4 cents worth of advice. I was referring to score shooting BR as well as group shooting BR. As you well know, retaining your zero, in a score match, is critical if you wish to punch out that tiny dot 25 times. Would I suggest using an action wrench and a barrel vise everytime? Yes, but not always absolutely needed.
Interesting thread which relates a little to something I've been thinking about... namely putting together a switch barrel rilfe... and I wanted to be able to set the barrels with 1 or 2 set screws. Hand twist them on to a preindexed point and then set the set screws. The screws would screw into/through the reciever into a nothched portion of the barrels thread, which would index it to the same point everytime you swapped it on.
Bad or good idea, and why?
125, 150 ft. lbs. or torque...damn that's alot. I've rebuilt a few motors in my day and usually torqued head bolts to 60. But then again motors and guns are...well to steal a phrase from Chad...like apples and oranges. Just curious how are you able to apply that kinda force...afterall it's not like you can slap a socket or a big wrench to the barrel...so how's it done?
It takes a barrel vice and a action wrench.
As I said I don't use but 50 to 70 ft/lbs because I dont wan't to load the threads any more
than nessary to keep it from working loose and letting the 60,000 PSI do the rest on the
I have torqued to well over 100 ft/lbs and found no advantage in accuracy .
I have owned 2 rifles that started shooting poorly and discovered that the barrel was only
hand tight. (They were torqued @ 30 ft/lbs) so I up the torque to 70 ft/lbs and solved the problem. (On actions with small tenons I drop the torque down a bit.
Everyone has there own idea of what torque is nessary and I don't think it makes that
much difference It's just a matter of choice.
J E CUSTOM