Introduction

I was watching some YouTube videos about how to convert a 12-gauge shotgun into a muzzle-loader to shoot black powder:

https://www.youtube.com/watch?v=pQN7XX6u2_Y&t=2s https://www.youtube.com/watch?v=5nzKLs03goo

In both videos the hosts are using a 12-gauge black powder adapter made by Short Lane LLC.  You can find their product here:  https://www.gunadapters.com/12-gauge-to-209-muzzle-loading-adapter-1/  Short Lane adapters are made of steel and they have adapters to fit any gauge shotgun.  According to the manufacturer, it is designed to take up to 80-grains of black powder and an equivalent volume of shot, absolutely no slugs.  It works best with break-open shotguns with barrels that have a modified choke; nothing smaller.

The design is very clever; it has an O-ring to keep the adapter in the chamber, and part of the rim is milled away to prevent the extractor from removing it from the chamber.  It uses a standard shotgun 209 primer as the ignition source, which fits loosely in the adapter and can be easily removed with a fingernail or knife tip.

I thought this would be a great idea for my double-barrel Baikel Bounty Hunter and single-barrel Winchester 37.  It seems rather silly to make a muzzle-loader out of a cartridge shotgun, but the adapter gives me the flexibility to still use my guns in case of shortages or in a survival situation.

An Alternative Adapter

Magtech makes brass shotgun hulls for just about any gauge.  These hulls take a large rifle primer rather than a #209 shotgun primer.  I thought these would make perfect black powder adapters with some modifications.  I would have to open the primer pocket so the primer would fit loosely, mill off part of the rim so the extractor would not remove the hull from the chamber, and mill a notch so I could use the tip of a knife or other implement to help remove the spent primer.  Hopefully this won’t be necessary if I open up the primer pocket enough so the primer falls out by itself.

Tools

I used my lathe to create an aluminum mandrel that fit snuggly into the mouth of the hull.  This prevented the hull from being crushed by the 3-jaw chuck of my lathe.  I also created a 1.000” x 0.500” brass collar that fit snuggly on the outside of the hull.  The jaws of my milling machine vise clamped on the collar which held the hull steady for milling without crushing or marring the hull.  The photo above shows the two tools and a completed hull.  Notice there are no marks on the hull.

Reaming the Primer Pocket

I placed the mandrel into the mouth of a hull and chucked it into my lathe.  I reamed the primer pocket with a 0.222” reamer so the primer would fit loosely in the pocket.

Milling the Rim and Notch

I left the mandrel in the mouth of the hull and placed the hull through the brass collar.  I placed the hull in my machinist vise and tightened the jaws against the collar.  I centered my table-top CNC mill on the center of the head, then milled off 120-degrees of the rim, and milled a 1/8” notch behind the primer pocket.  I made sure the edge of the hull was against the inside frame of the vise so I could use the vise as a jig.  I made two adapters for myself, and two for my friend Jon.

Preventing the Hull from Rotating in the Chamber
The Short Lane adapter has an O-ring which keeps the adapter seated firmly in the chamber and prevents it from rotating.  I discovered my adapters tended to rotate in the chamber which would cause part of the rim to get caught under the extractor and remove the adapter from the chamber.  The head of the case was too thin to cut a channel for an O-ring, so I tried an alternative method.

I put a piece of electrical tape halfway around the base of the hull.  Painter’s and masking tapes were too thin, and a complete wrap of electrical tape was too thick.  The purpose was to allow the hull to fit snuggly in the chamber without moving.  I needed to use my ramrod to remove the adapter from the chamber, but this is better than having it rotate. 

Loading
Dave Canterbury has a video on YouTube showing how to load the adapter.  He uses wax paper as the wadding, although both over powder and overshot wads are available online for purchase.

https://www.youtube.com/watch?v=txedePKtMu4

1. Insert the adapter into the chamber so the missing part of the rim is located above the extractor.  DO NOT insert a primer at this time.  Be sure to press the adapter all the way into the chamber.
2. Close the breech.
3. Pour a measured amount of black powder down the muzzle of the shotgun.
4. Tamp the powder down with a ramrod.
5. Place a wad down the barrel and tamp down on top of the powder with a ramrod.
6. Pour an equal measure of shot as powder by volume down the barrel.
7. Place a wad down the barrel and tamp down on top of the shot.
8. Open the breech, place a large rifle primer in the primer pocket, then close the breech.