Minimum barrel wall thickness?

[JDK]

I have acquired two old Getz swamped barrels.  They are unvented but have dovetailed tenons installed.  The dovetails are deeper than I would've done myself.

Here I have indicated the barrel wall thickness at the bottom of each dovetail from the breech face forward:

Barrel #1, 4 tenons:  Breech > (+8.5” = .140”)  (+11.5” = .115”)  (+24” = .072”)  (+34” = .062”)
Barrel #2, 3 tenons:  Breech >  (+13.5” = .130”)  ( +24.5” = .072”)  (+38” = .109)

I realize many of the guys are at the CLA show but......

What is the minimum recommended barrel wall thickness for safety?  Do these barrels meet that requirement.

Thanks,  J.D. 

[Acer Saccharum]

Golly, that's a tough thing for someone who's not a scientist to decide. I cut my dovetails shallow, particularly with a swamped barrel, in the thin waist section.

I can't tell you what's safe or not. Since you are expressing doubt, perhaps there is legitimate concern about the barrels.

[Eric Smith]

That's pretty deep, JD. What caliber and profile are the barrel?. That information might help someone who is experienced to give an opinion.

[Acer Saccharum]

To Eric's point, more info is needed, ie: barrel diam at dovetail, and caliber of barrel.

Obviously, it it's a 1 1/4" thick bbl, and the bore is .45, you can cut 1/8" deep dovetails and still be safe.

but on a 7/8 (.875) oct waist, with a .54 cal bore, that leaves a 1/8"(.125) wall.  If a .115 deep dovetail is cut, that's WAY too thin.

You're still going to get opinion, not science.

[JDK]

Those are not the depth of the dovetails they are the thickness of the barrel wall where the dovetails are.

#1 is a .50 with a max bore diameter of .510" and #2 is a .45 with a max bore of .460" measured land to groove.

I didn't measure to determine profile as I don't think Getz has a published chart anyway.  They have a nice gentle swamp and are each 42" long and each are breached properly as would be expected from Don.

Thanks, J.D.

[JDK]

Opinions are fine Tom.  I didn't expect science....I just don't know what the norms are.

I did several searches of old post before I posted this.  I found some recommended a .125" minimum bore but that was near the breach....I am well over that at that point.

The .50 is .062 just 3" from the muzzle and that is as thick as any fowler barrel so I would think that is OK.

The waist measurements of both barrels being .072" at 24" and 24.5" from the breech is what I am most unsure of.  I understand the bore pressures are much lower there than at the breech but is .072" thick enough?

Since I don't know what normal is, I don't know the answer.

Thanks, J.D.

[Long John]

JD,

I don't like rifle barrels with wall thickness less than 0.100 at the waist.  Call me chicken if you want but that is my minimum. 

Best Regards,

John Cholin

[boman]

Since I don't know what normal is, I don't know the answer.

 FWIW-I don't believe anyone knows the answer.  Everyone has an opinion, me included, and I suspect the barrels will be safe,  but, If they were mine, I would run a heavy proof load of powder w one ball,  unbreach and look for a bulge at the cuts.  Peace of mind is a wonderful thing

  Steve     

       
 

 

[Bob Roller]

I never cut a dovetail deeper than .080 regardless of barrel thickness.Usually .070 is enough to capture any sight.
On the caplock I tell myself I am making,I will dovetail the bottom flat about .080 for the barrel wedge or key
as some call it. I do use a milling machine for this job which guarantees accuracy.

Bob Roller

[David R. Pennington]

I believe I would proof fire them before I built a gun around them like Steve said. Then you will know.
I did a swamped GM .40 cal and I didn't feel comfortable cutting dovetails into the narrow waist. It was a 44" barrel and I used 4 wedges. The ones near the breech and muzzle I dovetailed and the two in the middle I soldered on.

[JDK]

I never cut a dovetail deeper than .080 regardless of barrel thickness......Bob Roller

Only one of these dovetails is cut deeper than .080" and just barely at .083"....leaving a .072" barrel wall thickness.

Measured breech to muzzle again, the dovetails are cut to the following depths:

.055"/.040"/.045"/.065" on the .50 caliber barrel and .050"/.083"/.047" on the .45 caliber barrel.

Obviously they are hand done and not machined.

I have read in the archives of the old site and pulled out this quote from Don Getz:  "Our standard Trans B or Golden Age
B barrels go down to .750 at the small part, and we do them in 50' cal., leaving you with a wall thickness of less than an 1/8 when you deduct the depth of the rifling.  We also make a 13/16 straight octagon barrel in 50 cal. which has a wall of less than .150, at the breech."

He goes on to talk about proofing these barrels with no adverse effects.  So, from that I can take it that .750" would be safe and just have to ascertain whether or not a few thousandths less wall thickness out front is safe.

I agree with Long John, in that I would be much more comfortable with at least .100" and I, as others, don't make a practice of dovetailing thin barrels.

I may just have to go over the mountain to pay Jon or Don a visit when they return from the CLA show.  Perhaps they would even aid me in proofing these barrels if I decide to keep them.

Thanks all and feel free to keep giving your valued opinions.  J.D.

[Robby]

A barrel maker once told me that "I like at least .070 wall thickness" in a conversation on this very subject.
Robby

[JDK]

That sounds like what I have been able to gather from the archives.

I have at least that on all but the one 5" from the muzzle of the .50 caliber barrel which is, as stated above, .065".

.065" is still thicker than the muzzles of my .62 caliber smooth bores.

Thanks, J.D.

[Naphtali]

If materials can be matched, Hatcher's Notebook, Book of the Garand, and P.O Ackley's two-volume book set on reloading include War Department (predecessor of DoD) tests of M1903 Springfield barrels, M1 Garand barrels, and Arisaka barrels.

One test I recall thinned a 30-06 barrel to .125 inch. It survived unlimited standard ammunition and several proof loads. One reassuring thing about information within these books is that identified barrel steels offer safety levels far exceeding any black powder barrel's requirements.

Hope this helps.

[Acer Saccharum]

Steel  is not stronger than driver inattention.

Two balls, one on the powder, and one short started caused this failure, right over a dovetail, co-incidentally.

[heelerau]

I would as others have said, proof test the barrels and then carefully examine them, even  getting a second opinion.
      You could also get die pen tested  if they survive proofing.  We have welds crack tested at work, and pipes thickness tested using non destructive techniques. Exraying the barrels would find any other faults as well.

cheers

Gordon

[JCKelly]

Little chevron (V-shaped) marks on a fracture surface point toward the start of the break. They point like little arrows to the fracture origin.

Best I can make out  from the photo is the crack started at the dovetail.

P.I.T.A. metallurgist

[Eric Smith]

Steel  is not stronger than driver inattention.

Two balls, one on the powder, and one short started caused this failure, right over a dovetail, co-incidentally.

Tom, is that one of your proofs, or just a picture you have?

[Acer Saccharum]

My loading while distracted. No one hurt. No steel left the barrel. I sent the pics with an article off to Muzzle Blasts mag.

The steel over the dovetail appears to be about .04. This is the dovetail for the front sight. Never had any problem with it until short starting a second ball.

The point being is that most barrels are perfectly safe with black powder, until you do something dopey like the above. The barrel may not have blown if a dovetail weren't right where the second ball was. It certainly would have bulged.

Highest pressure is at the breech. Once the ball gets going, the pressures drop off considerably. A heavy proof load will do little conclusive to test the web over the dovetails, but a second ball sitting at the dovetail will. But that's an unfair test for any barrel you want to keep.

[Roger Fisher]

Steel  is not stronger than driver inattention.

Two balls, one on the powder, and one short started caused this failure, right over a dovetail, co-incidentally.

Acer's incident caused me to check length of my short starter, which I then changed to have the started ball avoid the tennon notch.My starter lined up the started ball at said tennon notch not good in any event.  Good ol Acer didn't hide his incident but put it out here incl M Blasts to warn everyone he could...

[Eric Smith]

Looking closer at this pic, it appears the barrel is in a stock. If thats, true, were you proofing after you built the gun? Just curious!

[Acer Saccharum]

No, at a shoot.

Barrel long since proved its strength, which I do out of the stock.

This was while loading, and shooting, and TALKING, and thinking about too many things at once. No one got hurt. So it was a powerful lesson to me. I hope I can share some of that lesson with YOU, and may a little rub off on your shooting habits.

[Eric Smith]

So if I see correctly, You loaded once, then forgot you loaded the ball already, loaded another ball, but never drove it home, got distracted, then fired. Is that what happened

[Don Getz]

Nice picture Tom.   In proofing barrels, trying to create this type of blowup, the only way we could get them to bulge or
split out near the muzzle was to do exactly what you did.   We tried to duplicate this by just adding powder and short
starting a ball, in which case we could not get the barrel to bulge or blow.  It required a ball down on the powder and a
short started ball.  

Back to the barrels in question, it is very difficult to say what might happen.   Personally I don't think there would be a
problem with either barrel, assuming it would be loaded properly, and using common sense loads.  I have seen barrels
where the dovetais were cut too deep and it merely showed a slight dimple at that point.  Now follow this scenario.
When we first went into the barrel business we had all the tooling to produce a Nicholas Hawk swivel breech rifle.   We
made over a dozen of these units.  They were done in 45 & 50 calibres.  The barrels were straight tapered......800 down
to .700.     Using the mid point of the taper.....750, minus .520 for the 50 cal. and rifling, leaves a total of .230, or .115
per side.  Subtract .050 for dovetails, leaves you with .065....pretty thin but never had a problem with them......Don

[JDK]

Thanks Don.  I was hoping you would chime in on this.  I have had a couple of our neighbor builders give opinions also and they both felt as you. do....provided the routine percautions are followed.

Just so you know one of the barrels I procured was S/N'd in the 1500 range.  You made these quite a while ago, I would guess.

Thanks again to everybody who replied.

Enjoy, J.D.