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Double Rifles, Single Shots & Combinations >> Paradox and Bore Guns

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mart
.300 member

Reged: 20/01/04
Posts: 107
Loc: Alaska

Martini 12 bore project
#260776 - 20/02/15 09:41 AM

I posted earlier that I had picked up a pair of Greener Martini actions at a local gun show. I have made my mind up to build the first one into a 12 bore rifle, primarily for round balls but with the possibility of shooting some conicals. I believe I'll go with a straight octagon barrel.

I'm planning on using the Magtech brass shells and from what I understand they run more towards 11 gauge as far as internal dimensions for wads. Would that make it so a guy would need a .751 diameter ball, with the barrel having a groove diameter of around .741 or could I get away with a standard .729 12 bore diameter ball and the appropriate bore dimensions.

Thanks in advance guys.

Mart

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Longknife
.333 member

Reged: 17/04/08
Posts: 260
Loc: Illinois

Re: Martini 12 bore project [Re: mart]
#262231 - 14/03/15 03:06 PM

Mart, I do have some old Alcan and Fiocchi 12 ga. brass and they measure about .770 inside, more like a 10 bore. The plastic 12 ga. shells measure about .740. I would get the brass shells you intend to use first and determine what size slug/ball is going to be a good fit in those shells. Now we need someone here with more experience on bore guns here to advise on bore size......

--------------------
Longknife

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gungadoug
.333 member

Reged: 13/08/12
Posts: 285
Loc: NM

Re: Martini 12 bore project [Re: Longknife]
#262250 - 15/03/15 12:26 AM

I have a Greener Martini in a 12 bore rifle. I believe most available barrels will run around .736 or so- you will have to determine that when you get it in hand. Bear in mind that chambers for brass shells and paper shells can be of different dimensions! Whether you use brass or paper may depend on the actual bore diameter. In other words, a larger bore will be good with brass, where a tighter bore may need paper or plastic to hold the smaller ball correctly.

My Greener needs paper, I have a Lang double 12 rifle for brass, and the paradoxes all need paper.

So- my advise is to get the barrel first, determine what size ball it will require, then decide what shell to use that fits the ball best.

My 2 cents-- Doug

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mart
.300 member

Reged: 20/01/04
Posts: 107
Loc: Alaska

Re: Martini 12 bore project [Re: gungadoug]
#262275 - 15/03/15 08:30 AM

I had a friend mike his Magtech 12 bore cases that he just got. They run .751 inside diameter. The barrel I ordered will be .748 groove diameter and a 1 in 88" twist so I should be in good shape for a .750 or .751 round ball or short conical.

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Longknife
.333 member

Reged: 17/04/08
Posts: 260
Loc: Illinois

Re: Martini 12 bore project [Re: mart]
#262318 - 16/03/15 02:24 AM

Mart, what is the bore dia.? and where did you order the barrel from?

--------------------
Longknife

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mart
.300 member

Reged: 20/01/04
Posts: 107
Loc: Alaska

Re: Martini 12 bore project [Re: Longknife]
#262321 - 16/03/15 03:57 AM

Bore diameter is .728 with a groove depth of .010. I ordered a tapered octagon 4140 barrel from the Gun Works in Oregon.

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DarylS
.700 member

Reged: 10/08/05
Posts: 26822
Loc: Beautiful British Columbia, Ca...

Re: Martini 12 bore project [Re: mart]
#262322 - 16/03/15 04:23 AM

Sounds deep for a smokeless barrel - as if made on muzzleloading barrel internal dimensions. It won't be a problem, but makes me think even more strongly in terms of a .715" to .720" ball that is patched with denim - and loaded with black powder, of course.

--------------------
Daryl

"a gun without hammers is like a Spaniel without ears" King George V

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