Safety question

[Puzzledprofessor]

I may have really done it this time. I was cutting the dovetail for the rear sight on a 7/8 inch 50 cal barrel and it got away from me. The dovetail is now 75 thousandths deep. I measured the thickness of the barrel from the top of the flat to bottom of the rifling grove and got 180 thousandths. So, the question is, did I ruin the barrel? Thanks in advance for any answers. I just may have to buy my guns from now on.

[L. Akers]

I believe you are still good to go.  Consider that a 13/16, .45 cal barrel has a wall thickness of .181 BEFORE any rifling is cut and is considered safe in the rifled state.
 
Be sure the sight you put in the slot fills the slot completely.  This will add support for the barrel wall at the spot of the dovetail.

[WadePatton]

Don't give up just yet, there have been many minimum bbl wall thickness threads 'round here. I don't recall at this moment the average notion of the proper minimum, but that it's out there (here) somewhere.  And that's because people whoops! a lot, or think that they did.   

[coutios]

   Lets see....   .875  barrel dia.
                    - .500   Bore dia.
                    -.024    rifling depth  based on .012 per side
                    =.351  div.x2 = .176 wall thickness.
                     Minus .075 depth of dovetail = .101 = wall thickness...

         Is it safe?    Probably.. You feeling lucky???

      Just food for thought..... Dave

[M. E. Pering]

Why not just do a barrel test?  Put 3 times the normal load down the barrel, tamp a patch and ball down it,  fuse it, and run away.  Of course, this test should be performed with the barrel out of the stock, and all safety precautions observed.  If any bulging or splitting of the barrel is observed, it should naturally be rejected.  Don't forget to unbreech it and check there too.  With modern steels from reputable makers though, I doubt this will be a problem.

Matt

[ddoyle]

There is absolutely no way to answer the question with out knowing what the barrel is made from.

Start by finding out what you have. Then see what the Engineers and regulators say. C.I.P proof requirements is a good place to begin.

[oldtravler61]

My concern would be. How far forward from the breach is the slot?  (dovetail) The breach area is what absorbs the most pressure at the shot. With hunting loads I don't see a problem. Imho

[Puzzledprofessor]

The barrel is a green mt., so I assume the steel is as good as any and the dovetail is about 12 inches from the breech plug. Thanks to all who have responded thus far.

[oldtravler61]

Puzzeled if you check out page two of this. You will see where it was discussed. (Ok maybe 3) Hope this helps.

[sz]

Look at the cylinder of a 45 cap and ball dragoon or Walker revolver and see how thick the walls are.
WAY thinner than .175".  The Italian revolvers are not made from anything but the softest of steel.  They are usually only about .028" to .030"  They hold the pressure of 45 to 60 grains of black powder just fine. At 1/6 the thickness that you still have and the powder is directly under the walls of the revolver, not 8-12 inches behind.

So in all likelihood, you are fine.

Now there can be variables, such as an off-center bore.  If the bore is severely off center and if you were unlucky enough to have that thin wall at the 12:00 position there is a slim possibility that you may have a problem, so the advice given about is good.

What I would do is this:
Mike the barrel at the dovetail and write it down.  Load the barrel with a triple load of powder and tie it to a tire. Make a fuse and fire the barrel from a safe distance.
Now mike it again.
If the dovetail bottom is in the same place and there is no swelling at all, you are good to make your rifle on that barrel.

In the future when you are making a gun with thin walls start by cutting the sight and under-lug dovetails down to only about .040" I have done many with dovetails only .030" 
Install them and place a drop of acid flux on the joint.  Place a 1/16" long nib of solder on that joint and gently heat until the solder flows into the joint. If you have .030" of dovetail and solder the thing will never move.  You always want to zero the gun before you do the metal finish however in case you need to move a sight for windage.   Do all your zeroing before you do your final finish. 

[ddoyle]

so I assume the steel is as good as any

For what it is worth you could not be more wrong.

[jerrywh]

 I agree with ddoyle. What kind of barrel is it and who made it? What kind of steel is it.  Without knowing this all the other answers are irrelevant.

[Puzzledprofessor]

The barrel is a straight, Green Mt. I guess I was under the impression that they produced a well respected product. Should I be suspicious about the quality of their barrels

[ddoyle]

No one on this thread said anything about being suspicious.

You can either ask GM about it- Spend some time reading to educate yourself enough to feel confident - or pick which ever response above suits your wants.

[Mark Elliott]

I have had Getz and Rice tell me that .100" or more of metal in the wall of one of their barrels made of 12L14 was safe.  GM uses a harder alloy.   You should contact them and ask for their minimum safe wall thickness.   I think you are OK, but I have scraped a barrel before, that I wasn't absolutely comfortable with after such a mistake as yours.   

[Puzzledprofessor]

Thanks to everyone for their patient, quick and thoughtfull answers to a neophyte's questions. You all have been more than helpful.

DDoyle, I apologize for the use of the word " suspicious". It was not my objective to cast dispersions on what I am sure is a fine organization.

[M. E. Pering]

I have used GM barrels before, and see no problem with the quality of the steel they use.  I believe it is A.I.S.I. 1137.  They make a quality product.  I would use their barrels more if they produced them with profiles more in line with the period I build in.

Matt

[jerrywh]

 .101 wall thickness sounds bad but it isn't that simple. The dove tail has supporting metal on each side that is much thicker. How far up the barrel is the dovetail?? That is important also. Pressure drops a lot as the bullet  moves up the bore. 1137 is a very good metal for muzzle loading barrels.

[bob in the woods]

With the dovetail being 12 inches from the breach, and as it's a Green Mountain 7/8 in  .50 cal barrel, I personally, would fit the sight, proof the barrel with a stout load ...say double charge and two balls [loaded separately with NO space in-between them ]   Then move on.  I have seen some .50 cal rifled barrels that were only 13/16th oct and they were fine.