Barrel Thickness

[tiswell]

I am in the process of building a .54 caliber smoothbore, and I am realizing that it will not be complete to hunt with this season. I have an old .45 cal T/C Hawken with a barrel that has seen some pyrodex and was not cleaned at the end of every day (my fault).The barrel is not awful, but it is not pristine either. I am thinking of drilling, reaming and lapping the barrel of the Hawken to a .54 smoothbore. It would good to have both guns able to use the same components, and my son or a friend may want to chase after squirrels with me when I get the other one complete. Wall thickness at the base of the dovetailed underlug will be .118" at .54 caliber. Is this a sufficient thickness to consider it safe to shoot?

 

[hoochiepapa]

Welcome to the forum!!!
My Colerain smoothbore measures .185 at the muzzle. And I have Tom Grinslade's book on colonial fowlers, and most of them are 1/16" at the muzzle. About .065.
As far as that, it's all I know. I can't give you a gunsmith's opinion.

 

[paulvallandigham]

The general rule on barrel thickness between the bore, and any outside dimension( including dovetail slots and drill holes for underlugs or hangers) is .020" of steel, minimum. Yours sounds fine. Think of this: Notebook paper runs from .0025" to .003" thick. The minimum tolerance is 7 times that thickness. Your gun will have 5 times more than the minimum thickness.

Observation: Most people cut their dovetails too deep when making MLers. I always suggest that people look at the dovetails on modern guns, such as the Colt 1911, and measure how deep the dovetail is for the rear sight on top of the slide. It doesn't take much metal to hold a hanger securely. :hmm: :surrender:

And, remember also, that the stock is NOT supporting the barrel on most MLers. Its the barrel that is supporting the forestock. With an Octagon barrel, there is enough strength and stiffness to hold the small weight of a thin forestock, without going overboard with the depth of your dovetail slots. :hmm: :thumbsup:

 

[jerrywh]

In my opinion not thick enough at the breach end. But thick enough at the muzzle. I would want at least .200 at the breach. I wouldn't worry about the thicknes at the dovetail. I would worry about the thickness at the breach wall. The area at the dove tail has a lot of support from the surrounding area and the pressure put upon the dove tail spot is very small but the pressure at the combustion chamber is maximum and is of the utmost importance. There is a reason that thompson center makes their .054 cal barrels a larger diameter than the .045 and that is why.
I will have some photos of a mans hand and his thompson center hawken that blew up soon to show on this forum. Admitedly it was caused by gross stupidity but boring this out to a .054 is pushing your luck also. Note that the original wall thickness was about .202"
HOWEVER-- if you were to hold your standard service charge down to about 50 or 55 grns of ffg I think it would be OK but would go proof it with 150 grns of ffg and one prb about three times before I shot it. Or you could get one of the guys that says there is no need to proof the barrel to shoot it a few dozen times before you do. If you ever sell it be sure the next guy knows what the standard service charge is.

 

[paulvallandigham]

Thanks for the comment, Jerry. I must have misunderstood his description. I thought the measurement he gave was the thickness between the bore and the bottom of the dovetail slot- not the thickness of the entire barrel. Like you, I also would be highly alarmed at how thin this dimension would be back at the Breech of the barrel, where it receives the most PRESSURE when the gun is fired. Even .200" sounds a bit on the thin side, altho I have seen barrels that thin that were bored for 12 gauge shotguns. If you check the range of pressures for 12 gauge shells, or BP loads, you sleep a bit better with these old, thin barrels. But, I don't want someone trying to blow the barrel up with high pressure loads, either.

Thanks, again. Paul

 

[Zonie]

From my reading, I once found that back in the mid 1800's the Army ran tests to determine a good barrel thickness at the breech.

After much testing they arrived at .200 as being a good minimum thickness for the breech end of the barrels.

As for a .020 minimum thickness at a dovetail, to me that sounds much too thin, especially for the rear sight or a rear underlug that is near the rear of the barrel.

As the strength of a material is based on its tensile and yield strengths and the final strength is a function of the area of the material being stressed, multiplying a length by .020 greatly reduces the area under stress. In other words it severely weakens it.

Adding to this the fact that the relatively sharp corners of a dovetail are a stress riser further weakening the area I would say that even a value of .040 would be very marginal. .060 minimum would be a thickness that I would feel much safer with.

 

[Ft. Jefferson]

Nearly every barrel manufacturer out there offers 15/16", 54cal barrels. I have 2 from GM and use up to 100gr-3f in both of them with PRB. Your T-C 45cal is a 15/16" barrel! Bore it out and enjoys yourself.

 

[jerrywh]

Advise is easy if the advisor doesn't have to pay the price. This is kind of like someone telling you that if they were you they would divorce your wife. It has no effect on them.
Thompson center makes their .54 cal barrels 1" accross the flats. Why do you think they do that??? HUH?? #2 factor is this , when you drill out a rifled barrel it will not drill out very smooth because the riflings causes the drill to chatter. By the time you get that barrel reamed out smooth you will probably be closed to .580 cal.
If you do this I recomend sending it to alias Ft Jefferson and have him shoot it the first few dozen times. Try to visualize what your face will look like after a granade goes off 16 inches in front of it. Don't take advise from unknown strangers. Go call John Getz or Ed Rayle or Long Hammock barrel inc. Tell them Jerry Huddleston said hello.

 

[chuck-ia]

Drilling reaming and lapping, sounds easy. I don't think it's that easy though.Have a friend who has a similar barrel he put a liner in. Which included drilling reaming and lapping, (not so much on the lapping part) mostly drilling and reaming, he even has a lath, it didn't turn out so good. But, it will be a learning experience. flinch

 

[jerrywh]

Some companies do make 15/16" 54 cal. barrels.
I just doubt if you can come out with .540 bore when done. In any case if you do be sure to proof the barrel. Dixie gunworks catalog has complete info on proofing barrels.Another thing you might think about is the breech plug. How will that work out?

 

[hoochiepapa]

I thought he was talking about at the muzzle.
Sorry. :shake:

 

[tiswell]

Thanks for all of the replies! I apologize for the lack of introduction with my first post. I have been reading for so long I forgot that I had never posted here. I also apologize for the lack of clarity. The minimum wall thickness at the breech and the muzzle,(barrel is not tapered), would be .198".at the flat. It would be .271" at the octagon corners. The underlug dovetail is cut .080" deep which would leave a minimum wall of .118 between the bottom of the dovetail and the bore wall. I have a background in machining and expect that by creating the proper tooling I can pull this off. The point about T/C making their .54 caliber barrel 1 inch across the flats is well taken. Having said that, I see so many of the older muzzleloaders with barrels that seem much thinner then I will end up with. If I choose to go down this path prior to putting it into service I will remove the underlug, take some accurate dimensions, load it with 150 grains of powder and an ounce of shot, stick a fuse in the nipple, light it and run like the wind. Then recheck my measurements (if it is still together).If any swelling has occurred in the area, I will forget this folly, cut it up into little pieces and order a good prb barrel for it.

 

[rich pierce]

I'd fresh the barrel instead of going smoothbore.

 

[Black Hand]

I am in the process of building a .54 caliber smoothbore, and I am realizing that it will not be complete to hunt with this season. I have an old .45 cal T/C Hawken with a barrel that has seen some pyrodex and was not cleaned at the end of every day (my fault).The barrel is not awful, but it is not pristine either. I am thinking of drilling, reaming and lapping the barrel of the Hawken to a .54 smoothbore. It would good to have both guns able to use the same components, and my son or a friend may want to chase after squirrels with me when I get the other one complete. Wall thickness at the base of the dovetailed underlug will be .118" at .54 caliber. Is this a sufficient thickness to consider it safe to shoot?

Before you go through all the fuss the question to ask is: How does it shoot? Even though not pristine, if it shoots accurately, then I would leave it alone. Use it as excuse to order a smoothbore gun instead.

 

[jerrywh]

I can not find out wit hcertainty what thompson center makes their barrels out of but so far it looks like they are made from 4140. If that is true it is the best. You plan sounds good about proofing the barrel I suggest you proof it three times. with that load.
The guy that blew his thompson center up in Oregon a few days ago loaded it with one large load on top of another large load. This amounts to a bore obstruction. Knowing what he did he decided to fire the gun anyway. The result was a disaster. He's lucky he never lost more of his body than he did. All the spectators told him not to do it but he did it anyway. thay all stood way back out of the way. All the parts of the rifle were never found.

 

[Capt. Fred]

:shocked2: :shocked2: