Turning a double barrel 12 gauge into a muzzleloader.

[Alleykat]

I have a pair of very old 12 gauge sxs barrels, and I'd like to turn them into a sidelock percussion muzzleloader.
Has anyone done this? I've cleaned the barrels and the bores are pristine.

I figure that I can tap the chamber with 7/8-14 threads and make a pair of hooked breech plugs to fit. Then drill the retaining lug and pin it to a walnut stock that I've yet to make, throw on a pair of left and right percussion locks from track of the wolf, and presto.

I'm thinking of using around 80 grains of bp substitute, what should the proofing load be? I've read as little as twice a normal load, and as high as 4x.

Thanks, AK

 

[tiriaq]

Get a copy of "Recreating the Double Barrel Muzzle-loading Shotgun" by William Brockway. Detailed instructions describing what you want to do.
An advanced project.

 

[mooncoon]

In addition to what Tiriaq said, you want to think about how long you want your breach plugs. The recess in them will be smaller than the bore of the barrels and that is of significance as to how well the compression wad and shot column fit the bore without leaving a large space between it and the powder charge. While most shotgun barrels are about the same thickness at the breach (about .15" ) the outside diameter on some taper in quite rapidly ahead of the chamber and that may be a concern when converting

cheers mooncoon

 

[tiriaq]

Yes, beware barrel wall thickness where the front ends of the breechplugs seat.
Usually the barrel are shortened, removing much of the chambers, then the breechplug threads are cut. The noses of the breechplugs are machined to match what is left of the forcing cones. The breechplugs are counterbored, with smaller IDs than the bores. Make sure that this will not create an air gap between the powder and the wad, as mentioned already.
Making a traditional double gun is a serious project.
Barrel sets have also been used to make over/under guns. This can actually be easier. Conventional back action sidelocks, double hammer mule ear locks, or inline strikers can be used.

 

[Alleykat]

Thanks for the help.
I've checked the wall thickness at the thinnest point along the breech, and it is about .18" right at the start of the forcing cone. (It's .21 at the breech face.)
I plan on doing a 5/8" threaded plug with the 7/8-14 thread I mentioned, and leaving about an inch of round stock past the breech for everything to fit.
I'll post a picture when I get that far.