Barrel torque versus lub and calibre

[Tozguy]

Barrel torque versus lub:

In many of the discussions on how much torque to use in fitting a barrel, there is often mention of the use of a torque wrench and of how much torque to use. Little attention is given to identifying the lub used.
After reading how lub will change the torque rating on a ½’’-13 thread steel bolt;
• No lub, torque rating in the order of 120 ft-lbs.
• Using SAE 20 oil, the torque rating drops to 87 ft-lbs.
• Using SAE 30 oil, the torque rating drops to 83 ft-lbs.
• Using graphite and oil, the torque rating drops to 62 ft-lbs.
I wonder whether we should leave lub out of the discussion. I realize that barrel threads are larger and finer than the above example but the principal should be the same. Is the use of lub (anti-seize included) generally recommended on barrel threads? If so, it seems that when we compare our barrel torque level without relating it to the lub we are using, we are comparing apples to oranges.
If someone changes lub but carefully torques to the same level as before using a torque wrench, could there be a change in the loading of the threads and would this potentially have an effect on accuracy?

Barrel torque versus calibre:

As far as I know, the torque required in a particular thread application depends on the loading and the metal’s strength and elasticity. Everything else remaining constant, would you torque a 222 barrel to the same level as a 300 WSM barrel? If not, why?
If a barrel is torqued to a level of below that dictated by engineering standards for that set of conditions, how much impact do you expect it might have on accuracy?

I apologize if this stuff has already been flogged somewhere here. I am doing my homework on switching barrels and have not turned up satisfactory info along these lines. Your comments would be greatly appreciated.

 

[Preacher]

If you dont use a good lube on the threads you'll stick one in a hurry, and it's not fun tying to undo the problem...

 

[RonAKA]

Great question. I have industrial experience in high strength bolting, which I am quickly forgetting since I have retired. If I could find them, I have formulas for calculating what you are asking. But here are a few general comments:

- The relative torques for the lubes you gave are right in the ballpark. A good anti-seize compound containing copper or nickle will reduce torques to at least half normal, and a bit better than graphite and oil. Motor oil is a poor lube. It does not really work in brass resizing, and if you were stuck for a lube a resizing lube would be much better than motor oil. In industrial applications it is common to measure the length of bolts before and after torquing to measure stretch. A better lube gives the same stretch with less torque. A common value for coupling bolts is 1.5 thou per inch of length (measured center of thread area to center of thread area). This results in about 45,000 psi tensile stress in the bolt.

- In industrial applications you do use anti-seize compound and it is believed that this results in tensions that are less likely to back off, and make it easier on the thread surfaces.

- The effect of finer thread is to get more stress with less torque. Also the larger the thread diameter the more torque is required to get the same stress.

- I'm not a gunsmith, and don't know what practices generally are. But I would suggest torque should be based on lube used and the thread diameter and thread pitch -- the cartridge the barrel is chambered for should have nothing to do with it.

- If you get a chance read the book Rifle Accuracy Facts by Harold Vaughn. His belief is that a significant part of factory gun inaccuracy is caused by slight barrel to action movements from shot to shot. He uses a Remington and does a bunch of tests to prove his theory. He goes on to claim you cannot torque a Remington enough to prevent the movement, before you destroy the threads. He even came up with an improved thread design to allow sufficient torquing. I'm still chewing on whether or not this conclusion is strictly valid. We know many using switch barrels do not use a lot of torque at all, and shoot great targets. This however may be a function of how carefully fitted the threads in the barrel are to the action. Perhaps if they are highly accurate, and the barrel is very straight, then a slight movement of one relative to the other results in very little inaccuracy?? Don't know. But, it does show you should put as much torque on as you can, and an anti-seize lube would help.

- Vaughn also agrees that a jam nut system like the Savage is a better arrangement for eliminating movement. I believe there are conversion to this system for standard barrels. May be worth considering.

 

[Tozguy]

Ron, thanks for info. I have read Vaughn's book and refer to it often. What is written in Chapter 6 on Barrel-receiver threaded joint motion concerning the importance of axial preload on the threads to stabilize the joint (p.109) is revealing. Part of my questions relate to the statement on page 112 about axial preload having to be in excess of 24,000 pounds to assure that the joint cannot move under extreme conditions of heating, shock and vibration.
Vaughn used more sophisticated equipment than I do. Hence a secondary question relating to how good a shooter do we have to be to detect joint movement from our accuracy results. Can there be joint movement without our knowing?

 

[TRECustom]

I started off with the idea that a precision tenon to receiver thread fit was beneficial for at least 2 good reasons. More intimate contact between the threads lets the receiver ring do a better job of supporting the chamber area of the barrel tenon (reduced diameter) when a round is fired. A precision fit also helps center and stabilize the barrel with reasonable make-up torque. I probably go too far, but I stop cutting when the receiver will barely start on the tenon, and lap it on with 800 grit garnet. It takes time, but the garnet doesn't imbed, is easy to clean out, and when you finish, the fit is silky smooth, but the receiver has no wobble with 2-3 threads made up.

When I first pull a barrel out, I clean most of the gunk out of the receiver threads with a tap made from an old barrel, brush them with a small brass wire wheel in a Foredom
handpiece, wash them in Varsol, and blow them dry with air.

Before make-up, I wipe a thin coating of light gun oil on the tenon thread. I don't use any kind of grease, and I haven't had any galling. 1.062" threads get 80 - 90 ft/lbs of torque, and 1" threads get 70 - 80 ft/lbs. I haven't done many barrel jobs, but I have had to pull 3 barrels back out after make-up to cut extractor reliefs in them. All 3 made back up to the match mark wthin 5 ft/lbs. I figured I'm not reaching yield strength, but am getting good solid make-up. I came up with these values because when I did it, I kept increasing the torque until it felt right, not because I had any scientific data.

I agree with the other replies: torque should be determined by thread diameter, length, pitch, lubricant used, and material strength, not caliber.

I may hack off some Savage guys, but I don't like the nut. It reduces the diameter of too much of the barrel, and isn't as precise as a hard shoulder. I've never barreled a Savage, but if I ever do, I'll do it like a Remington. Again, no science, just my humble opinion.

One more thing, I watch Preacher's and RonAkA's posts. Good chance to learn something.

There are guys that do this for a living who know a whole lot more than I do about how to thread and make up a barrel. This is just how I like to do it. No science, but maybe it'll help you decide how you want to do it.

Good luck, Tom

 

[Larryh128]

I use basically the same technique as Tom for finishing a thread with the same idea that full thread engagement is vital to a good shooting barrel/action. What I have seen though is a tendency to thread easier every time the barrel is & off.
Right or wrong I use anti-sieze.

 

[TRECustom]

Larryh, I wouldn't mind using neverseize because of its greater lubricity, and it's the old "that's what I'm used to" syndrome more than any objection to it. I would think that neverseize would be similar to oil and graphite, so using Tozguy's info, all I'd have to do is back off about 20 ft/lbs of torque. Probably be just fine, but it would feel weird to me. Something reassuring about 70 - 90 ft/lbs on a rifle barrel. To repeat, no science, just opinion.

Tom

 

[Tozguy]

Much appreciate the input folks but I am still stuggling with the calibre question. It relates to how hollowing out a bolt will change its torque rating. Loading a bolt usually stretches it and a hollow bolt should stretch more everything else being equal. This extra elongation in the thread area could lead to a different (maybe uneven) loading on the threads at a given torque value. The bigger the hole through the bolt the greater the potential impact on thread elongation under loading.
Appling this logic to the original context, with a given barrel diameter at the breach end of say 1.250'', there will be significantly less metal in the chamber wall on a WSM than for a 222. Should I understand that both joints will nevertheless act the same under the same preload torque and under the load from firing?

 

[lelongcarabine]

Many moons ago I learned to fit barrels by the measure try,feel,measure method. The torque was translated into shoulder crush. Thread cutting was executed with hand ground HS threading tools, between centers and many measurements using PD thread wires. Break down, try, re-setup, chase, measure, etc. Sometimes a dummy barrel extension was turned from bar stock and threaded just to get the perfect fit and measurements.
The crush fit used was commonly.002", calculated into the barrel extension length and the headspace(chamber depth). We started out with high pressure center lube as a thread lubricant. I gravitated to High Temp antisieze in later years. I've never stuck a barrel. Stainless Steel is NOTORIOUS for gauling especially in close fitting threads. This method has worked great for me over the years. Greg

 

[BoydAllen]

I hate to rain on your parade, but the most accurate rifles on the planet are generally made up with a generous thread fit and in most cases installed by feel. I have the utmost respect for Vaughn,but these are the facts. Also, most custom actions are stainless, as are most of the match barrels in use. Under these conditions, fitting a thread too tightly, and/or assembling without proper lubrication is an invitation to galling, and having to cut off the tenon and drill and bore to clear the action threads. If you are getting much rotation beyond the point that a barrel is hand tight, something is out of square. I have four barrels that are fitted into my short range Benchrest rifle. I can interchange brass between them all, and when switching between them, do it by feel, with the thinnest coating that I can manage of antiseze on the threads, and bolt grease on the shoulder. I have built many engines, and am very careful about how I torque bolts when doing so. Tightening, and fitting barrels to custom or properly blueprinted factory actions, is a different situation. Teen aggregates have become fairly common at benchrest matches. You might consider this before rejecting what I am telling you.

 

[TRECustom]

I pay attention to what benchresters do because of your knowledge of building, shooting, and cleaning extremely accurate rifles, and have no argument with the way yours are built and made up. However, I do see Tozguy's point about the effect of caliber on thread fit and barrel makeup torque.
For me, there's no way I would put together a .338 Excalibur, a 7 STW, a .270 WSM, or even a .220 Swift, the way that you describe. As nearly perfect thread fit as I can get and 80 - 90 ft/lbs makes a lot of sense to me. A fairly loose thread fit and hand makeup don't. My smallest bolt gun caliber is a 220 Swift, but I cut it and made it up exactly the same as the boomers. As far as accuracy goes, with a SAAMI std chamber, the best I've got so far is 5 rds (#21 - 25) into .328" at 100 yds. still testing ammo, but my homemade .30 x .378's best is 5 rds into .204". and the best .30 x .378 I've personally witnessed is 5 into .091". The barrels are Lilja, Hart, and Shilen respectively. In my case I'm always the limiting factor. My point is that they were chambered with a SAAMI or factory dimension reamer, all have very close fitting threads, and all were made up at 80 - 90 ft/lbs with light gun oil in the threads and on the thrust faces. I've pulled several barrels that were cut and made up that way, most were stainless, and a couple had stainless receivers. I may just be very lucky, but as Terry Bradshaw said, I'd rather be real lucky than real good. If I ever do feel one galling, I'll instantly switch to neverseize, and back off on the torque.

Old guys do get long-winded, but this turned out to be a good thread, with a lot of info in it. Hope it hasn't made it harder for Tozguy to decide what to do.

Good shooting, Tom

 

[BoydAllen]

I am pleased to hear of your success. My point was not that a close fit would prevent accuracy, but that it does not seem to be a requirement. I will ask my friend, that has a switch barrel wildcat, based on a .338 Lapua how his barrels feel when he is installing them. He has shot under a quarter inch with the barrel that is .338 bore. I do have one question. Why did you choose to use SAAMI spec. chambers? Also,those few friends who have had seized threads tell me that by the time they felt anything, it was too late. Evidently, your choice of oil has worked out, but I can think of no reason to not use a product that has been specifically designed for the task. Oh, I forgot to mention, I wouldn't think of just snapping a barrel tight by hand. I use a T handle rear entry wrench, that only engages in the front receiver ring, and my barrels are tight.

 

[TRECustom]

BoydAllen, good reply. I messed up on the hand tight issue. You never said hand tight.

I'd like to hear what the guy with the.338 Lapua says.

I'm not sure why I'm not having a problem with galling. Maybe because I rock the receiver back and forth and bump the shoulder as I make up, and can feel any change in the resistance. Rocking back and forth may allow the pitch faces to get fresh lube too. Another possibility is that a true shoulder and true receiver face will go from 0 to hard in about 10 degrees of rotation. That doesn't allow much rubbing (surface heating) before hard makeup.

I use the SAAMI std reamers mostly so that commercially available ammo will work in the chamber, and for my purposes, the SAAMI dimensions haven't hurt accuracy. Also, I cut minimal headspace chambers, and the SAAMI spec reamers still allow for easy chambering of factory or handloaded ammo. Frequently, my chambers won't take a go gauge, but will chamber commercial ammo or handloads smoothly. The only time I deviate is if a rifle may be used for dangerous game. Then I try to hit go + .003". You want everything to chamber in it.

In the case of the Weatherbys, I use factory dimension reamers, with all that freebore, because it is safe to use factory loads or hot handloads. I am familiar with a couple of rifles that were chambered with custom short throat reamers. One was a .30 x .378, and the other was a .338 x .378. The Weatherby factory ammo was too hot for the short throats and both rifles blew primers, gas cut the bolt faces, and had hard extraction. The 30 by bent the floorplate with one of the factory rounds. Violent. The owner had to shoot watered down handloads until he had the barrel set back and rechambered with a factory dimension reamer. I don't know what became of the .338 by. It's worth noting that the five boomers I've talked about are / were all on MK V actions. The worst thing that happened was when the 30 by blew the floorplate open, it gave the guy a stinger that he still had when he left the range. Of course, his nerves were toast too. (I'll never know why it didn't break the stock and hurt him).

Of the two .30 x .378's I mentioned in my last reply, one is mine and the other belongs to one of my family. I used the same reamer for both, He's just a better shot than me. I also have a homemade .338 x .378 that I need to work on since I decided to shoot only 300gr Smkhp's in it. Hard to imagine, but the factory 225gr Barnes X load shoots 1/2 moa at 200 yds all day. I just don't want to shoot that light a bullet in the rifle. It also is a factory dimension chamber. I have to single load the 300gr loads. One is 3.9" oal, the other is 4.0" oal. Oal to reach the rifling is 4.19". The 300gr is the only bullet that can reach rifling. 250's have no neck engagement left when they touch. The 225gr factory load jumps approx 0.31" to reach rifling. The Weatherbys taught me that if I cut a tight, round, concentric chamber, the freebore doesn't hurt accuracy.

The way all this applies is that close fit threads and solid torque on makeup don't hurt either. It doesn't sound like we're that far apart, we just have rifles intended for different purposes and approach them differently.

I'm the world's worst about getting off subject and getting long-winded, but I'm glad you jumped in. I'll bet Tozguy is too.

Good shooting, Tom

 

[Tozguy]

Yes, I'm very happy to read you all. Much appreciate your contributions. Hope more is coming. Will come back soon with some related stuff.

 

[butchlambert]

Pay attention to what Boyd is saying! Most of what is posted here on this is superfluous.
The shoulder is not going to move hardly at all or any between 40# or 125# of torque. Stainless on stainless can gall. I have witnessed it. It ain't pretty. My data is empirical, but I have barrels with both and loose threads and they shot well regardless.
Do the best you are capable of in maching and spend the greater part of your time learning to read the conditions.
Butch

 

[therifler]

hi boyd , i subscribe to the same method for barrel fitting as you do. rear entry wrench with t-handle seems to work well. i do not go for a real tight fit on the threads and have never used lube of any kind . i have been building for better then 29 years it is my profession and have not had a barrel sieze ever. i don't know how much torque i am putting on the barrel as i go by feel but my t -handle is only 15" long . i never had a barrel turn off and the rifles seem to be pretty accurate . i do all my fits the same even on the 375 RUM.
if i would have to put a torque value to it between 50-70 foot pounds . by the way back when i was in school they did tell us that lube does influence the torque value. T.R.

 

[Tozguy]

Its taking longer than I expected to talk a couple of mechanical engineers into running some stress tests. They do it for a living in the aeronautical industry and maybe their input would be interesting.
Not questionning what has been written here, just curious about what a stress analysis might show.

 

[BoydAllen]

The Rifler,
You build rifles with stainless components that are assembled with no lube at all? I doubt that there is a rifle, barrel, or action manufacturer that would recommend such a thing, and I am pretty sure that they would warn not to. The most accurate rifles in the world have their barrels assembled by feel with lube on the threads. I have a friend that has a long range hunting rifle in a LARGE magnum caliber, made with stainless components. It is a switch barrel, and he uses a wrench to assemble the barrels to the actions, with lube, by feel. The gunsmith told him to snug them down, back them off a little, and then give them a "snap" to final tigntness. The larger bore of the two barrels has shot five shots into slightly under a quarter of an inch. I have seen the group. and I have seen him shoot the rifle. It is wonderfully accurate, and he is very skilled, especially considering the recoil. Engineer all you want. As far as I am concerned, the matter is settled.

 

[therifler]

i certainly not telling anyone to change their techniques by what i say . all i am saying is i do not need any lube when i assemble my rifles and have not had a problem . now i would not say that about a switch barrel where you are removing the barrel on a regular basis. i do not build switch barrel rifles .
As for accuracy no one is complaining boyd PM sent .have a nice weekend guys . T.R.

 

[shortgrass]

Just for a little info on backgound, I've been threading/installing barrels for a bit over 20 years , now. Both S.S. and CM. I've never used a lubricant. I've never had any galling problems. My threads won't 'hand snap' nor do I have to use a tool to turn them to the shoulder, I strive for a 'happy medium' in that respect. I polish the thread with a rubberized abrasive block (1"x2"x6" 240grit) while still in the chuck. I clean both threads (internal & external) or any lube of foreign material before assembly. If oil/lube is trapped in the thread, and in the case of CM, it is to be blued, either 'hot' blue or slow rust blued, the oil/lube will weep from the thread (out of the front base screw hole) ruining the blue job (will leave 'spots', may ruin the bluing bath too). Same goes for the modern coatings. GunCoat, DuraCoat, or Ceracoat will not stick to anything with oil/lube on it. Any of the finishes I'm aware of require cleanliness to the max. Switch barrels probably need to be lubed, because of repeated assembly/disassembly. The finish on the two mating threads may or may not be relevent. This is just my experience (I've threaded/installed 9 barrels so far this year). No, I'm not an engineer. Do it the way that makes you happiest! just my two cents