doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com How much metal is bored out when sleeving bbls?

Judging a process based on a bad quality example doesn't give an accurate representation of any process' capabilities.

A sleeving fit of barrels intended to be welded should be a close slip fit. That is; the fit should be withing a few thousandths or less. Ideally, it would be an interference fit. No flapping in any area would be possible. A good fit is important with any of the processes.

Typical Sn/Pb solder has about a 7000psi ultimate tensile strength at room temp. That drops dramatically as temperature rises. At 140F that drop in tensile strength is in the area of 30%. I don't have data above that temp other than the flow temp is 360F. More specific to the sleeving process is shear strength, since most of the surface area is on the o.d. and i.d. of the parts. The solder above, has about a 6000 psi shear strength. I don't have the decay on the shear strength vs. temp, but you can bet it tracks with the tensile. Remember, most of us will shoot a gun till the barrels are well above boiling at least on some occasions. Let's just be conservative and say you shoot it until it's hot enough to drop the shear strength by 40%. That leaves 3600 psi shear strength.

I'll swag the diameter of the sleeve joint at say... .900". Let's use 3" for the length of the sleeve joint. That gives us about 8 1/2 sq/in of surface. That gives us a strength of the joint of about 30,000 lbs. The problem with solders is "creep". At elevated temps, a sustained or repetitive force will cause creep. That's an incremental amount of strain (movement) do to time, load, and temperature.

On a weld, the ultimate strength is maybe 70,000 psi. The remaining weld after dressing down the outside is probably 1/16". The O.D. is about 1" at the 3" point on 12ga barrels. You can only weld about 85% around the barrels because they are close together. So, you end up with .16 sq/in of weld. Which comes out to about 11,000 lbs. But then there's the breach end that gets welded as well. That is probably worth about half of the other weld because it's in shear. So maybe 16500 lbs for the strength. Barrels just don't get hot enough to decay steel strength to any meaningful amount or at least not if you use the temperature we are comparing with the soldered example.

So, you're right that a soldered barrel is stronger if you consider that you only get the barrels hot enough to decay the solder strength by 40% and you have 100% solder joint for 3" of the tube.

The real question is: what are the forces pushing the barrel out of the breach assembly? I'm guessing they are pretty low. The success of both methods over the decades has validated this. It's just the friction of the payload going down the barrel and thru the forcing cone and choke from what I gather.

As you may have guessed, I sleeved a barrel set using TIG as the joint method. I was going for the asthetics of no visible joint.

Lets take a look at this from a simplified design point of view. The barrel has two forces to resist: the radial gas pressure and the forward axial force caused by wad friction with the barrel walls. The most useful formula for resisting radial stress is the hoop stress formula - stress equals pressure times inside radius divided by wall thickness (there are good calculators available via google). One such calculator says for a chamber pressure of 12,500 psi, an inside diameter of 0.729", and wall thickness of 0.150" the stress would be 30,375 psi. I feel sure that tube makers would use steel with working strength well above that number. I have a sleever Woodward boxlock with 0.160" walls at the face and 0.115" at the seam 3.25" from the face. Safe? It carries 3T / sq inch proofs. Note that the original barrel stubs will, indeed, carry load. The sleeve steel will quickly expand to fill any void due to less than contact fit (think press fit). Then, the original stub will start to pick up load.

The axial (forward-backward) force will be caused by the wad to barrel wall friction. Since the front of the barrel is open, there will be no chamber-barrel pressure force in the forward direction. The wad drag is in the backward direction, so the barrel to stub joint must resist it. This resistance must come from the solder or weld plus (and this one is the big hitter) the steel to steel friction of the joint. If we have 10,000 psi of chamber pressure and the steel to steel friction coefficient is 0.2, we will have available 2,000 pounds of force per square inch of joint surface. Note also that this force will build up as the pressure builds in the chamber. That means that the resisting force will be available before the wad hits the barrel. I think the weld/solder is going to carry very little firing force.

DDA

Whatever everyone thinks,Ideally the gap between the two parts should be filled with something even if its a modern adhesive.

I notice that none of the monoblck barrels are welded

I remember reading a long time ago (maybe in a very early DGJ) that a gun was fired with the sleeving blanks in breach unsoldered and they did not fly out.

Proper radiusing of the breech ends and barrels can create an invisible joint without resorting to welding on the barrels.

The French developed the "cannon frete" system, where the monobloc is shrunk onto the barrel to avoid the theoretical problems of the barrel leaving the monobloc. The same system is used in artillery pieces. Practically the problem of the barrel leaving the monobloc seems to be nonexistent. Primitive zip guns prove that barrel and cartridge recoil in one sealed unit backwards. There are some intersting vids of such deviceson Youtube which cast doubt on some old theories re action flexing etc during firing.

There is also the option of threading the barrel into the monobloc. The Baby Bretton has threaded barrels which can be changed by mere hand pressure.

My Pieper hammer gun marked Modified Diana has the tubes threaded into the Mono-Block.
Pieper's original patent which results in the "Step" at the end of the block had the tubes inserted from the breech & wth a taper. Many Piepers one sees built with this construction are marked Original Diana. Not much posssibility of tubes with either of these assembly methods moving forward.

This thread is an example of why I read the Doublegun BBS.I learn something every day.Thanks to all.

Breech, not breach.

Ideally, there should not be any gap to fill.

Regarding monoblock barrels made in production guns: Welding and refinishing would be counterproductive to efficient production methods, cost/time savings, etc., which are always high on the list of production items.

I would not be surprised if there are monoblock guns being made that are simply interference fit.

Pugwash , I don't know who dose the sleeving you refer to but if it is done correctly the tubes should be a drive in fit . NO gaps . I recently saw a sleeved gun that had been tinned ,the tubes were coming out ,when cleaned off for re tinning there was a .006" difference between the tube and the back end and had relied solely on the tin to hold them together . Had to have new correctly fitted tubes . Some mono block guns ,Beretta for example tin the tube into the mono block and I have known these to come loose as they are not a tight enough fit in my opinion ,but having said that it is a very rare occurrence give the number made.Others like Miroku and other Italian guns appear to be silver soldered /brazed as are the ribs . As with every thing else there are good jobs and bad jobs .