Just wondering if barrel torque to the reciever of bolt guns has ever been seriously studied.

Yes, in some ways it has been. Harold Vaughn, in his seminal work Rifle Accuracy Facts, shows his results from both instrumentation readouts AND actual group sizes when comparing methods of threading and torquing barrels for accuracy.

He put some new colors in my own paintbox (grin), I recommend the book highly.

Bottom line is that he shows that a different thread form will yield far better results than any largely-imaginary (IMO) 'optimum' torque value.

As a matter of interest, many Benchrest barrels in the past have been torqued so lightly that moderate hand pressure would seat and release the threads, allowing quick range comparisons of different barrels under the same weather conditions. Sinclair markets a special hand vise for this purpose.
Regards, Joe

I was reading some testing on another website (I can't remember which one) and the work done on there said that 35 ft-lbs was all that was needed to hold the barrel rigidly on the common action threads.

quote:

Originally posted by J.D.Steele:



As a matter of interest, many Benchrest barrels in the past have been torqued so lightly that moderate hand pressure would seat and release the threads, allowing quick range comparisons of different barrels under the same weather conditions. Sinclair markets a special hand vise for this purpose.
Regards, Joe

I've read that in those circumstances hand threading the barrel in til it goes "thunk' suffices IIRC.

Yes snug is tight enough. What I was pondering is to what extent the accuracy is affected at different torgue values.

quote:

Originally posted by tin can:

quote:

Originally posted by J.D.Steele:



As a matter of interest, many Benchrest barrels in the past have been torqued so lightly that moderate hand pressure would seat and release the threads, allowing quick range comparisons of different barrels under the same weather conditions. Sinclair markets a special hand vise for this purpose.
Regards, Joe

I've read that in those circumstances hand threading the barrel in til it goes "thunk' suffices IIRC.

From actual experience I can tell you it IS true. One of my benchrest guns I used for shooting cast bullet benchrest on Saturdays (.30 BR) and jacketed bulet benchrest (6m/m Talldog) on Sundays every month for several years. I just turned one barrel off and screwed the next one on, hand-tight.

For one thing, if the barrel is right hand twist, every shot you fire will tend to tighten the barrel more, rather than shoot it loose. That meant in actual practice that even though I just turned the barrels on hand tight, I had to use an inside-the-action wrench to snap them loose each time I went to change from one barrel to the other.

It also meant I carried a very small aluminum barrel vise and a large C-clamp as an integral part of my shooting kit. That way I could remove and replace barrels at the range on days I wanted to do that.

The procedure was: 1. Clamp the vice to the shooting bench. 2. Tighten the rifle into the vise by the barrel. 3. Snap the action loose from the barrel. 4.Unscrew and remove the barrel. 5. Screw the replacement barrel in place by hand only (no vise, no wrench). 6. Resume shooting.

I DID see a 7 m/m Remington Mag chambered barrel shoot loose on the 1,000 yard line in a high-power match at Palomino Range, Sarcee Barracks, Calgary, Alberta one year during the Alberta Provincial Championships.

Up to that point, the shooter had been leading the two-day grand agg, but he had several consecutive increasingly worse shots out of the bull in the last event of the two days before he figured out what happened and had to withdraw from the tournament.

He was a gunsmith from Kamloops, B.C., who outsmarted himself.He over-thought all the "edges" he could acquire over the competition to win the match, so he installed a left hand twist barrel (but still standard threaded) in his action

Supposedly, the left hand twist would counteract the natural drift of bullets to the right over long ranges when shot in North America. That part semed to be true and was working out for him. But, unfortunately, two days of long heavy slugs slamming into the left hand twist of the barrel under high pressure snapped it loose, and it commenced to unscrew itself exactly when Murphy would have wanted it to...at the most critical time.

No such problem for all the other shooters who used right hand twist barrels. He was DQ'd. They all at least finished with whatever scores they'd fired in the matches.

Sometimes it pays to just go with acquired skill rather than to over-rely on technology.

I thought the point of it all was to make a RIGID connection between barrel and receiver ??
Back in ancient times when I was in gunsmithing school I was very careful to cut the thread so it had a very snug fit .Don't remember what the torque was.The rigid thing was extended to glass bedding the stock to also make a very rigid receiver/stock connection.

quote:

Originally posted by mete:
I thought the point of it all was to make a RIGID connection between barrel and receiver??
Back in ancient times when I was in gunsmithing school I was very careful to cut the thread so it had a very snug fit. Don't remember what the torque was. The rigid thing was extended to glass bedding the stock to also make a very rigid receiver/stock connection.

The heavily torqued kind of rigidity is one way to approach making a stable, accurate rifle, but torqueing the barrel and action very tightly together is not the ONLY way to produce sufficient stability for superb accuracy. Good, close-fitting threads of a proper form is another contributor to stability. Good bedding is yet another.

As in every other kind of "cat-skinning", there is more than one way to build an accurate rifle regardless what was or is taught in gunsmithing schools. If there was only one successful approach, there would only be one successful "secret combo" out there. We all know that isn't the way it is. There are many useful contributors to accuracy which can be applied in the practical world.

quote:

Originally posted by mete:
I thought the point of it all was to make a RIGID connection between barrel and receiver ??
)

Exactly! Vaughn shows photos of sectioned threaded-shoulder attachments using standard vee-form threads, and the pics clearly show how it's virtually impossible to achieve total rigidity without changing the actual thread form itself.

Vaughn's demo photos show that the first 3 threads bear almost all the load, leaving the rear several threads free to vibrate and thus increase the total amplitude displacement of the muzzle end.

By using a modified interference-fit thread form, Vaughn was able to reduce the amplitude as measured by his instrumentation. Surprise surprise, he also reduced his group size accordingly as measured on the target (grin)!

IMO anyone interested in accuracy and practical ways to achieve it should read Vaughn's book. Even if you don't agree with some of his conclusions IMO the smithing info alone is worth the time, and anyone contemplaring an underground or enclosed range will surely learn some new things.

BTW his test mule is an old Remington 721 chambered in 270 WCF. No exotic BR actions or special PPC chamberings in this book, just good practical info on a good practical hunting rifle using good practical techniques explained in a good straightforward and simple manner.
Regards, Joe

This has become a very informative thread. Just as I had hoped.

I lieu of useing a modified thread for could a thread compound (one that dries hard) such as what is found when a remy barrel is unscrewed by used instead?

quote:

Originally posted by J.D.Steele:


IMO anyone interested in accuracy and practical ways to achieve it should read Vaughn's book. surely learn some new things.

Joe

Agreed. One of the more interesting (to me) things I found in his book was his experiments with concentricity of action features.

As a result, I designed an action which is almost 100% concentric in so far as openings in the action, locking lugs and their recesses, scope mount bases, recoil lugs (yes, it has more than one), trigger hanger and so on. I asked a well known gunsmith to help me make the action, and he agreed. He then checked with BATFE and then reluctantly declined to get involved.

BATFE ruled that I could build it entirely by myself for myself without a manufactuer's license, but even if I hired a person (that gunsmith) to help with some of the machining in my shop, then any such employee would have to obtain a manufacturer's license even though I still wouldn't need one myself.

They said that is their interpretation of the law and its regulations even if the person employed by me never removed the action from my shop at any time, did not do the major portion of the work, the action was never finished during his employment, and he never fired or otherwise used the action.

At that point I said to hell with it and went on with my life without even building a working model. Life is too short to spend it arguing with government morons.

If it worked out, I would have been happy to assign a right to use it to the military advanced marksmanship/sniper units for any use they might have found for any of the features.

BTW barrel threads are quite short and one gun ,originally a sniper rifle has a 2" thread !! Steyr SSG

Vaughn also showed that a barrel loosened when
heated and caused random strays. It took only
a little loose. He was a bench shooter.

modified interference-fit thread form

a match between the size and shape of two parts, such that force is required for assembly as one part is slightly larger than the other

quote:

Originally posted by tin can:
modified interference-fit thread form

a match between the size and shape of two parts, such that force is required for assembly as one part is slightly larger than the other

Basically Vaughn's solution was to form a slight ledge at the bottom of the thread form, by offsetting the cutter as the thread approached full depth. Sorry it's been many years since I last read this book so the precise mechanical details of the operation are unclear, but you get the point.

The offset ledge engages on each and every thread as the barrel is threaded into place and thus provides at least a modicum of additional hard-surface support and vibration dampening for the rear threads.

Apparently it works, at least it worked for Vaughn.

I've used, and seen used by others, epoxy and Loctite on the threads. Seems to me that the gain was not worth the effort, at least not for me. I'm not gonna say that there was no improvement at all but it was mighty small and inconclusive in my mind, and the adhesive WILL cause any future smith to scratch his ole head when he tries to remove the barrel (grin)!

Please be advised that excessive torque on a thin shank will cause a tight spot in the bore or chamber at that point. Probably not worth any consideration on most bolt rifles but some single shots have mighty thin thread shanks.

Repeated excessive torquings can also cause Brinelling of the contact surfaces and thus lead to future problems as the steel deteriorates. This is the main reason folks use washers under bolt heads (grin).

Those of you who have rebuilt auto/truck engines have experienced the effort required for a 35-45 lb torque value on the engine's con rod caps. IMO this should certainly be sufficient and maybe even a little much for a rifle barrel, depending upon the front face engagement contact % at the receiver ring.
JMOFWIW, regards, Joe

Rather than argue the point too much farther, I'll simply say that my shooting associates and I have set over a dozen national records in benchrest competition and all four of us regularly switched barrels on our rifles just as I described in my previous post in this thread. Some 15 of those score and group national records still stand, and at least one of them has stood for 14 years now. We also won the Grand National Championship in cast-bullet benchrest at least 4 times between us and our names are engraved on the large national championship trophy cup displayed at the Whittington
Center each year during the Nationals.

So theoreticians can debate and posit dicta all they want. More than hand tight torque is NOT essential to accuracy if the rifles are otherwise systematically set up to produce accuracy and the shooters know how to shoot.

Personally I've never seen a published torque spec for a barrel. Other then say an AR 15 or something of the sort.

In all the books I've got not one smith says anything about torquing a barrel.
I'd have to say tight enough to hold the barrel on for your intended purpose.

quote:

Originally posted by J.D.Steele:
Those of you who have rebuilt auto/truck engines have experienced the effort required for a 35-45 lb torque value on the engine's con rod caps. IMO this should certainly be sufficient and maybe even a little much for a rifle barrel, depending upon the front face engagement contact % at the receiver ring.
JMOFWIW, regards, Joe

IMHO, that much torque MAY set up stresses detrimental to accuracy. Not always, but at least sometimes.

If I was going to torque a barrel to a receiver, I would limit the torque to something more like 40 INCH pounds, not FOOT pounds.

There was a day when some gunsmiths, armories, and companies commonly torqued barrels to receivers with enough force to create a .003" crush fit. Hopefully, those days are past for most of us who are seeking maximum accuracy from our rifles.

quote:

Originally posted by Alberta Canuck:
There was a day when some gunsmiths, armories, and companies commonly torqued barrels to receivers with enough force to create a .003" crush fit. Hopefully, those days are past for most of us who are seeking maximum accuracy from our rifles.

I'll certainly NOT argue with that statement!

Actually the better alignment provided by the more-precise Benchrest machining methods does result in a much stronger and more rigid joint with much greater contact area at the ring abutment. This greater and more-precise contact area permits the barrel to remain firmly held when only 'snapped' into place by hand pressure alone.

Don't expect this 'snap' to hold most non-BR barrels, though. It's only the precise BR machining methods that permit the joint to remain effective at such a low torque value.

For a little further background, urban legend has it that the 1914/1917 Enfield rifles were commonly assembled by clamping the barrel and receiver in 2 opposing chucks and then spinning them together under power. This method was used because The Powers suspected that the Enfield's LH twist would ultimately cause loosening. Well, maybe it held the barrel just fine but it's also a fact that sometimes an Enfield receiver ring will be found with tiny cracks apparently from the sudden socking-up shock as the surfaces met under power.

Today most rifles are still assembled with a crush of up to 0.002"-0.003" in some cases, depending upon the tolerances. B-U-U-U-T-T, remember that most rifles are NOT machined closely enough to allow any other method during mass production.

That's why BR smiths stay in business RE-machining factory receivers!
Regards, Joe

Generally speaking I agree with your most recent post in this thread, Joe.

The only place we differ is in the degree of torquing force which must be applied. I do not believe ANY crush is needed. Because almost all rifle barrels one buys in the U.S. these days are right-hand twist, those barrels will not shoot loose if snapped together by hand, assuming even reasonably decent machining. The more one shoots them, and the more powerful the cartridges used, the tighter they will torque themselves together. But that usually does not produce any "crush" that I have seen or measured.

Of course, as a by-product of our discussion in this thread, you have mentioned one of the most important accuracy features regardless what other accuracy tricks are used in building a rifle...precision machining. Precision machining in everything...making the actions, making the barrels, making the bedding units if metal is used in them, fitting everything together, and so on and so forth.


Precision is also critical in fitting the brass to the chamber, so we all neck-turned our cast bullet BR cases to where they conformed to an approach I would definitely not recommend for either hunting rifles, jacketed bullet shooting, or for other than skilled-machinist rifle users...a very light interference fit of the case necks to the chamber neck walls. That was only in our cast bullet guns; we left about .0005" per side or .001" overall clearance on cases used in our jacketed bullet BR guns.


That is why three of the four of us I mentioned as shooting benchrest together each did our own rifle building, including chambering, throating, threading, etc. The fourth being a multi-millionaire had all his rifles built by Jim Borden..he had a least half a dozen Borden-built rifles with jacketed bullet barrels at one time. David Lee chambered, throated and fitted the cast bullet "switch barrels" for him using my reamers.

We would all each also turn our brass to within .0001" or .0002" neck wall thickness of a dimension we determined for our individual chambers. Because neck turners leave tiny grooves and ridges, we would actually turn our brass near to .0001" or .0002" larger than what normally shot best...a few fire-forming shots would iron out those ridges, giving a very slightly thinner case wall. Then we determined which of those cases to shoot in the important matches by an age old technique not involving any more fitting....just seeing which cases shot best on practice targets.

But, a further discussion of BR rifle accuracy development techniques does not belong here in this thread, so I'll quit the "tricks" part.

I just still believe from my own experiences that a crush fit of barrels is not only not required, but is sometimes harmful to the search for accuracy.

Anyway, best wishes to you. And I fully understand that different approaches to the subject work best for different people. There is NO ONE BEST WAY in a subject as complex as rifle accuracy.

It would be gruesome to watch a higher speed video of a Mauser rapidly torqued to provide .003" of crush.

For Remingtons (sorry) I like the idea of that receiver tightening piece that fits in where the bolt head would otherwise. Use an Aluminum barrel fixture/clamp as alluded to earlier. Put a cheater bar on the receiver fixture and just let it drop (once you have barrel and receiver in contact). That might be just enough, but not too much. YMMV/FWIW/MOO.

I think we're talking apples and oranges here to some degree. I will certainly agree that a 'snap' is certainly enough to seat the well-machined barrel into the equally-well-machined receiver. Remember, with all that good machining you can expect 98%+ contact at the shoulder with a mere snap of the wrist.

While with some factory fitups, you would be lucky to be able to seat the barrel at all fully without using a clamp or wrench of some sort. Initial surface contact at the shoulder is often less than 25% until after the initial crush or 'draw', and the final 'draw' is frequently ~1/16"-1/8" depending upon the thread pitch.

BTW thread pitch varies from a low of 8 tpi (Ballard) up to around 20 tpi (several). We know that this wide a variance in pitch examples will certainly require a different amount of 'draw' throughout the range of examples used. Same physics laws apply as with any threaded connection, the fine-threaded ones require a different torque value as opposed to the coarse-threaded ones.
Just a few further reflections, regards, Joe

quote:

Originally posted by lawndart:
I like the idea of that receiver tightening piece that fits in where the bolt head would otherwise. Use an Aluminum barrel fixture/clamp as alluded to earlier. Put a cheater bar on the receiver fixture and just let it drop (once you have barrel and receiver in contact). That might be just enough, but not too much. YMMV/FWIW/MOO.

You've just described the Sinclair setup, except I believe that their L-wrench is aluminum rather than steel. BTW even the steel L-wrenches I've seen have NOT been able to stand up to military barrel removals, all that I've seen used will distort under a shock load. I'm sure that someone could readily make a properly-heat-treated L-wrench but I've never seen one.
Regards, Joe

I have one of the aluminum "L" wrenches, but I also have a steel "T" wrench. The "T" wrench replaces the bolt when in use, and exerts force internally on both sides of the action up at the locking lug area.

If I have an action which for some reason some one of my friends wants more tightly torqued than just a hand "snap", I use the T-wrench. Screw everything together within maybe 1/8th turn of being in full contact,then snap it together with the wrench.

With the T" wrench I don't think there is as much danger of bending an action or otherwise ending up with some unbalanceed application of force as with the "L" wrench...plus there's not nearly the same danger of bending the wrench itself. Just my opinion of course, YMMV.