How does one get enough barrel joint torque on a Savage?

[frwillia]

Reading Vaughn, he is looking for something like 20,000 lbs of tension load in the barrel/receiver joint. I need to sit down and do the math but I'm thinking that's close to 500 ft-lbs. I can coat the joint with assembly lube, hang my body on the end of a cheater and get that torque if i machine it with a shoulder instead of using the barrel nut. My problem is when I need to use the barrel nut.

The barrel, nut, and receiver all need to be managed to get the torque with out screwing up the headspace adjustment.

Anybody have a good technique to do that?

Thanks
Fitch

 

[PEI Rob]

Lube and torque it to 100 just like anything else. Tightening the nut pulls the barrel from the action, you will add about .002" headspace after tightening the nut. The guys here say 100 lbs for a shouldered barrel, the nut at 100 is the same. IIRC, the factory uses 75.

 

[frwillia]

Lube and torque it to 100 just like anything else.

Thanks for confirming the .002". I measured that and wondered if that was "standard". I'm surprised the factory only uses 75 ft-lbs.

I lubed it with assembly lube and torqued it to 150 ft-lbs, but that only puts just under 6,000 lbs of tension in the joint, which isn't enough to stabalize it. I realize my .22-250 (which the barrel in quesiton is) won't have the forces that Vaughn's .270 did, so it will probably shoot OK, but I'd like to be able to do bigger cartridges as well.

My problem isn't applying the torque, it is doing it to the barrel nut with out shifting the receiver and affecting headspace.

Torquing a receiver against a shoulder is easier because there are less degrees of freedom.

I think I'll just make a setup that bolts to the mill table with the same CL as the barrel vise, use that to hold the receiver, constrain it to prevent rotation but let it move along the barrel axis and see how that works.

Fitch

 

[SGS]

How does one over torque a barrel on a Savage?

Years ago I bought Vaughn's book and read it with great interest. At this point, I don't find myself doing anything that I can attribute to his findings. Any creditable smith will tell you that you don/t need 500 foot pounds of torque on any rifle barrel joint. We don't all agree on exactly how much, but somewhere around 100 up to maybe 150 foot pounds is about the maximum that most of us use. Factory barrels are sometimes tightened much higher.

If you decide to tighten to 500 foot pounds anyway, you will need to finish ream to final headspace afterward by hand in order to remove the constriction in the chamber.

When is the last time you have seen the name "Vaughn" as gunsmith on a benchrest match equipment list?

Scott Roeder

 

[flatlander]

Man, Fitch, 500ft./lbs. is waaay too much torque. Maybe that's the value Howa uses to torque their factory barrels onto their 1500 actions - I've never managed to break one loose, even with a 3' cheater over the handle on my Brownells action wrench. I'd be very concerned about damaging the action and/or chamber using 500ft./lbs.

 

[frwillia]

Years ago I bought Vaughn's book and read it with great interest. At this point, I don't find myself doing anything that I can attribute to his findings.

So far I'm not doing anything other than making sure my bullets don't have any eccentricity and trying to make sure my barrel is tight that I'd attribute to his findings. But then I'm on my first time through the book so it's all news to me.

Any creditable smith will tell you that you don/t need 500 foot pounds of torque on any rifle barrel joint. We don't all agree on exactly how much, but somewhere around 100 up to maybe 150 foot pounds is about the maximum that most of us use. Factory barrels are sometimes tightened much higher.

I took it to 150 ft/lbs with lube. That's the tightest I could get it with out going to extraordinary measures. I'll try that and see how it works.

The first time I put it together I followed the directions that came with the Wheeler wrench and torqued it to 40 ft-lbs. It shot well through breakin and for a couple of groups after, then the groups started to open up and get erratic in a way that suggested a mechanical issue. When I took it off to true up the front of the receiver it didn't take much at all to get it loose. I thought "oh oh" maybe that explains the growth in group size. So I wanted to get it tighter.

If you decide to tighten to 500 foot pounds anyway, you will need to finish ream to final headspace afterward by hand in order to remove the constriction in the chamber.

I'm not sure that's right, but it could be. I hadn't thought of that so thanks for bringing it up.

I am going to see if I can figure out a good way to get more preload tension in the joint. The limiting condition for tension is the strength of the first couple of threads. The chamber itself is much stronger.

When is the last time you have seen the name "Vaughn" as gunsmith on a benchrest match equipment list?

Scott Roeder

I was with you right up to that last question.

I don't expect to see his name on a bench rest match equipment list. Come to think about it, why would I expect to see his name on a benchrest match equipment list?

He retired in the mid 1980's having fought in the Korean War, so presuming he was in his sixties then, he is in his late 80's or early 90's now if he is still with us. He never was a commercial gunsmith as far as I know, and was mostly interested in hunting rifles. He did the research because he is a trained research scientist, believed in data, and wrote a book that could be duplicated by any independent researcher looking to confirm or dispute his results.

What he did is relatively unique in the accurate shooting world. He published a book based on documented research that could be duplicated - no old wives tales, no anecdotes, no name dropping, no claims - just instrumentation, hypothesis, data, adjustment, and more experiments, and conclusions all of which were tracable to his data.

It doesn't matter all that much if what he did was right or wrong, it is documented, can be disputed by those who have the data, and the general knowledge base will improve.

There are folks who build winning rifles, and folks who don't, and it's a good bet that neither knows why in any way they can prove tracable to basic physics with the rigor Vaughn used in his book. They may know how they did it, they believe what they did is "the" way to do it, and they may have won some matches, but they still may not know why it works, or doesn't, as the case may be.

Knowing how and knowing why are quite different things.

Fitch

 

[frwillia]

Man, Fitch, 500ft./lbs. is waaay too much torque.

Yeah, that was pretty much my reaction when I did the arithmetic! I sat down to figure out what it would take to get a barrel as tight as he said it needed to be and that is the answer I got. Actually, he said it needed to be 5,000 pounds of pre-load tighter than the threads would take given the joint design. I really hope I can get this rifle to shoot with out having to tighten it any tighter than I have it now (150 ft-lbs).

Maybe that's the value Howa uses to torque their factory barrels onto their 1500 actions - I've never managed to break one loose, even with a 3' cheater over the handle on my Brownells action wrench. I'd be very concerned about damaging the action and/or chamber using 500ft./lbs.

I am concerned about that as well.

But I am still interested in how a person would go about doing that with out screwing up the headspacing. It may be it can't be done. In any event, I don't think anybody is going to be able to answer the question because it's becoming clear almost nobody has done it.

The loads associated with a .270 (what Vaughn was experimenting with) are quite a bit more than for my .22-250 or .243win. Probably not 75% less, but less. In any event, the rifle is together, for now, and I'm hoping for a good day to go to the range.

On the up side, we did have to mow the lawn last week for the first time this year, which is more promising than if we'd had to plow snow.

Fitch

 

[SGS]

Apologies to Harold Vaughn

Quote "When is the last time you have seen the name "Vaughn" as gunsmith on a benchrest match equipment list?" was of course a rhetorical question.

After I posted this morning, I thought that I may have sounded harsh or critical of Harold Vaughn. I got the book out and looked through it for the first time in years and I was reminded of how much I enjoyed reading it the first time. What he did was impressive, approaching the accuracy question with a scientist's analytical view and then actually performing laboratory testing of his hypothesis'. Much of what he covers is very accurate and widely respected.

Sometimes scientifically valid findings simply prove to be irrelevant in the harsh light of the testing laboratory that is competition. No disrespect is intended to Harold Vaughn.

It often happens that gunsmiths and machinists have opinions about the things they do that are not supportable by scientific evidence and may even be wrong. Much of what they do works, however, and the proof is on the targets. I can pretty much guarantee that not a single known benchrest gunsmith in any benchrest discipline torques barrels to 500 foot pounds. I have also not heard of any of them adopting the "Spiralock"(tm) threads that Vaughn advocates. One manufacturer of benchrest actions used the tapered receiver threads that Vaugn recommends for a short time, but stopped, not because the tapered threads didn't work, but because some gunsmiths, not being aware of the tapered receiver threads, had difficulty with them

Scott Roeder

 

[brian roberts]

The one fly I found in the...............

soup, was the statement Vaughn made that, "....if it groups 1" at 100yds, it'll group 2" @ 200, 3" @ 300, 4" @ 400, etc. etc." which I have not found to be borne out in shooting. Now, this discussion you two are having, is just maybe, for me, another bug in the lunch. No, after reading the book at the library, I didn't buy one.

 

[frwillia]

Sometimes scientifically valid findings simply prove to be irrelevant in the harsh light of the testing laboratory that is competition. No disrespect is intended to Harold Vaughn.

Yes. There are times when scientifically valid findings are irrelevant, regardless of the discipline in question. I saw it again and again during my 35 years in Aerospace.

It often happens that gunsmiths and machinists have opinions about the things they do that are not supportable by scientific evidence and may even be wrong. Much of what they do works, however, and the proof is on the targets. I can pretty much guarantee that not a single known benchrest gunsmith in any benchrest discipline torques barrels to 500 foot pounds.

I believe that is a true statement. I'm not surprised either. Apparently it isn't necessary or it would be done. A lot of phenomena aren't black and white. In production there are variations, sometimes the only place things work is when performance fringes overlap, other times (reliable repeatable performance) it is the opposite.

I have also not heard of any of them adopting the "Spiralock"(tm) threads that Vaughn advocates. One manufacturer of benchrest actions used the tapered receiver threads that Vaugn recommends for a short time, but stopped, not because the tapered threads didn't work, but because some gunsmiths, not being aware of the tapered receiver threads, had difficulty with them

Scott Roeder

I also don't see anybody using his redesigned barrel joint that could be stabalized by a lot less preload.

But I am sure enjoying reading his book. It is to rifle shooting like Marchaj's "Aero Hydronamics of Sailing" is to the sailing folks (I read all Marchaj's books too).

Fitch

 

[frwillia]

I went back to be sure I hadn't read the book wrong.

Vaughn never actually wrote the 500 ft-lbs number. I calculated that using his equation applied to the geometry of my barrel joint. I asked myself if I calculated it wrong. I could have.

I had done a quick calculation while drinking a cup of coffee and eating a cookie (I'm a cookie monster) and I might have gotten it wrong. I don't usually, but if I had it wouldn't have been the first time. I found the scrap of paper in the wastebasket, double checked what I did, and using Vaughn's published equation and friction factor I got the same number, 471 ft-lbs which I rounded up to 500 ft-lbs. I also noticed that he says in one place that 250 ft-lbs gives him about 10,000 pounds of preload which, even though he had a different thread pitch, correlated with what I got doing the math. OK, I did the math right.

Studying the equation, there is one coefficient in it, the coefficient of friction between the mating surfaces in the joint, that is a bit uncertain. He used 0.24 lb/lb, and so did I when I ran the numbers. I wasn't expecting a debate (though i should have been ) so I just used his number.

I looked that coefficient up in Machinery's handbook and found that number to be on the high side. Most values for lubricated metal are between 0.07 lb/lb and 0.15 lb/lb. So I did some parametric evaluation of the equation, that is, I substituted different likely values of friction coefficient, and got some interesting numbers.

In the table below:

• Tmax is the torque in ft-lbs to get to 20,000 pounds of joint preload, which Vaughn says is about all the threads will take based on his analysis of the strength of the threads.
• F is the axial preload in pounds resulting from 150 ft-lbs of applied torque.
• f is the friction coefficient in lb/lb. The conditions for the friction coefficient are at the end of each line - from Machinery's Handbook, 25th edition, page 1403. This is for bolts and nuts, but it should be close.

• f=0.24 lb/lb Tmax=471 ft-lb F=6,336 lb This is Vaughn's value for friction factor.
• f=0.15 lb/lb Tmax=300 ft-lb F=10,000 lb This machine oil lubricated steel
• f=0.11 lb/lb Tmax=224 ft-lb F=13,440 lb Moly disulfide grease
• f=0.07 lb/lb Tmax=150 ft-lb F=20,042 lb Graphite in Petrolatum or Oil (AKA Assembly Lube, which is what I used)

Sorry the table is so hard to read, but this forum editing sw isn't table friendly.

That being the case, this second assembly has the threads at some place between 13,440 and 20,000 pounds of preload, probably closer to 20,000, which is about as close to perfect as one can get if the goal is 20,000 pounds but no more. The first time I assembled it I was probably closer to the 6,300 pound number because the joint had only residual oil lubrication. I was lucky I didn't gall the threads! I won't do that again. I used the assembly lube the second time mainly to avoid the possibility of galling since it is a stainless nut on a stanless barrel. Assembly Lube is good stuff. Gritter's uses a lube sort of like it in his video. Ed Franklin doesn't.

I wish I had done this evaluation before I torqued the joint, I would have if it was going in a space craft, but the end result, serendipitous as it was, is about as good as I could have gotten, so I'll take it.

Standard practice, as I pick it up here based on the discussion that accompanied the "snap tite" discussion, is to torque to around 100 ft-lbs. Depending on what lube is used, this results in between 6,674 and 13,610 pounds of preload. That may be enough given the reduced forces from the relatively wimpy (compared to a .270Winchester) bench rest cartridges. It may also be that some of the high end bench rest folks, who don't publish what they are doing, are using torque values closer to 150 ft-lbs and assembly lube, which gets them up much closer to 20,000 ft-bls.

I don't have any indispensible ego attached to any of this, so have at it.

Fitch

 

[PEI Rob]

Fitch, I'm glad you mentioned friction versus preload, I didn't want to bring it up and sound like a dick. Not sure about cut threads, rolled threads, frictional properties of grease etc but I can tell you in my unprofessional experience clamping force is a wild guess. I didn't read Vaughn, why 20,000? The bolt thrust is MUCH less than that. Your .475" [worst case senario] chamber has a square inch area of .177" and a gross overload of 70,000 lbs and ZERO friction makes 12,390 lbs thrust. The barrel threads are still preloaded against the same side of the V as the dynamic load even though the nut threads are not. I'm not disagreeing with Vaughn but I would need more discussion before changing my thoughts on this. Too many guys use around 100 lbs/ft of torque with lots of friction in the joint and do well. I will admit the next time I install a barrel it will be about 120 and I'll smirk when doing it.

 

[jGEE]

Mr. Fitch i certainly don't know but maybe you might have a feel of sorts. Since the statement "let there be light" -how many discovery's have been accidental as opposed to purpose?

Maybe a bit off topic but, my guess would be more than half?
joe

 

[frwillia]

I didn't read Vaughn, why 20,000?

I had a chance to look up the answer to your question. Vaughn's summary of the loads tending to destabilize the barrel joint. These are from Chapter 6 p112 in the version I have.

Cold barrel
Recoil Lug 1,500
Bolt Thrust 5,400
Chamber Radial Expansion 10,000
Total 16,400

Hot Barrel
Recoil Lug 1,500
Bolt thrust 5,400
Chamber radial expansion 10,000
Differential temp expansion 7,000
Total 23,900

Vaughn's assessment is that 25,000 lbs of preload is required to stabilize the joint but that the threads will not take more than ~20,000 lbs.

Fitch

 

[Big Al]

48" pipe wrench would be my guess, a tripod pipe vise would be good also. Ridged is my flavor of choice. The aluminium is a lot more handy for hauling back and forth to the range!

 

[frwillia]

48" pipe wrench would be my guess, a tripod pipe vise would be good also. Ridged is my flavor of choice. The aluminium is a lot more handy for hauling back and forth to the range!

Universal chain wrench? Receiver in a pipe vise?

Seriously, I should have asked how to get up to 18,000 to 20,000 pounds of preload - it turns out that is relativelly easy. Use a lavish coating of graphite in HP lube, AKA assembly lube, and torque it to 150 ft-lbs. Approach 150 ft-lbs with care under those conditions, it is possible to strip the receiver threads if over done.

Fitch