Converting old Thompson barrels to smoothbore? Shotgun sizes?

[yakipreacher]

Hi...
I have a couple of old shot out Thompson Center barrels. I am wondering if anyone has ever reamed them out to turn them into shotguns? Or smoothbore? One of said barrels is 15/16 across the flats and the other is 1". What would be the safe bore size for each barrel. The 15/16 is currently 50 cal rifled and the 1" is 54 cal.
Any help would be appreciated.

Thanks
Jerry

 

[Rusty Gunn]

There is no hard rule because there is a large variation in the depth of the rear sight holes as drilled and taped by T/C from barrel to barrel and year to year resulting in many barrels with thin material between the threaded rear sight and the bores. Also depth of rifling and concentricity of bores varies. It is best to use the recommendation of whom ever you choose to reborn you new smooth bore. Don’t want to risk blowing up a barrel that close to your eyes.
YMMV

 

[Grenadier1758]

Reboring of barrels is not one of the do-it-yourself tasks that I would recommend. Best to contact someone like Bobby Hoyt the make the assessment and recommendation for your barrel.

 

[8 BORE]

Better to be SAFE than SORRY !
T/C made some smoothbore barrels for their rifles. Maybe you can find one to fit your breech plug

 

[Carbon 6]

Reboring of barrels is not one of the do-it-yourself tasks that I would recommend. Best to contact someone like Bobby Hoyt the make the assessment and recommendation for your barrel.

Bobby can also re-bore/rifle or re-line those barrels and turn them back into tack drivers.

 

[Loyalist Dave]

Well I'd think about turning the 15/16 barrel back into a .54 rifle with Mr. Hoyt's help, and the 1" thick barrel into a 24 gauge smoothie, with Mr. Hoyt's help. That gives you a good deer rifle, and a good shotgun (or a good .58 cal smoothie if you can get close enough to the deer). NOW IF you live out where the elk do roam....reverse it and get a 28 gauge in the 15/16...and the 1" into a .58 rifle.

LD

 

[yakipreacher]

So... what makes it risky if you have reamers? Is it the depth of the screws for the rear sight or are there other risks?

 

[Eric Krewson]

I will take a stab at it. As I understand it you have to have the tooling to move your reamer through the barrel at a very consistent speed or you will have tight and loose spots.

 

[RonT]

I'm considering a similar project, and as mentioned above am skeptical of holes and/or dovetail depth by others.
My project is a Turkey gun using the T/C breech plug mounted to an octagon to round barrel. Will be following this thread.
Cheers,
R

 

[burlesontom]

You can do this yourself with simple hand tools. You can use a round rod close to bore diameter. You may need to have one end turned down to fit the chuck on your hand drill. Cut a slot in the the other end of the rod and put a wrap of emery cloth in it. Feed it down the bore to polish out the rifling. The rifling in TC guns is noted as being shallow. Maybe .006 deep. It will take a while to do and once the rifling is polished out use finer and finer grits until the bore is smooth. Be sure and pump the rod in and out just like you do when honing a cylinder. You will not remove enough metal to worry about the sight screw holes.

Then if you want you can use a reamer. Determine the bore size you now have. Maybe close to .512 or so. Then go to a tool store and buy a reamer just slightly bigger and have them send it to a grinding shop and they will grind it to the final size you specify. You will have to have a rod bored the size of the shank on the reamer for an extension. You could weld it on but would grind a flat on the reamer shank and drill and tap a couple of holes on the extension and use a couple of set screws to lock them together. That way use can use the extension for the larger bore if you want to.

Don't worry that you can't get the last half inch or so of rifling out at the breech end. You will never know its there. I have been looking for a rusted out CVA or other cheap BP rifle to do this very thing myself. This is exactly how I would do it. I worked all my young life in my dads machine shop and have done other jobs similar to this. I wish he were still here and still had the machine shop. This would be a piece of cake with an engine lathe.

Now I promise you before long someone is going to come along and say this will not work. But it will. I have done similar to a could of shotguns to relieve some of the fixed chokes. No problems.

 

[8 BORE]

T/C used to make a 56 smoothbore barrel maybe you can find one.

 

[Dave Marsh]

I have sent 3 to Bobby Hoyt and simply told him to bore them out as large as he can and still have a safe barrel. I am happy with all 3. About $120 a barrel.

Dave

 

[8 BORE]

Ok

 

[yakipreacher]

Dave/58 Caliber.... What size did he bore them out to? TC actually produced a 12 gauge in a round barrel for a New Englander.... these aren't round though. Just curious......

 

[Dave Marsh]

He was able to get them to 58 caliber. Two are smoothbore and one is rifled, One was percussion so I sent a flint TC tang along and converted it. I had to drill the flash hole. Can't beat his work and turn over was around two weeks,

Dave

 

[8 BORE]

You did well