Used a Snider type breech.They were many old muskets converted in this fashion to become cheap shotguns. Widely sold by mail order houses such as Sears in late 1800's and early 1900's. Zulu was one of the most common trade names used and has become a genereic term to identify the breed.
ZULU is correct. Several gunmakers in Belgium and France would take old worn out surplus military muzzle loading muskets and convert them to a breech loading single shot shotguns by cutting off the breech end of the gun and fitting some sort of side swinging breech block and boring out the barrel to a shotgun gauge. They would also bend the hammer over to strike the new firing pin. These guns were originally intended to be sold to natives in Africa hence the ZULU name. Of course they made it to the United States where they sold for as little as $3,00 each.
The story is in three parts:
1. French military muzzle loading rifled musket of around .69 cal.
2. French military conversion of muzzle loading muskets to make breach loaders. Many of these were used in the Franco Prussian War because there were not enough bolt action needle guns in French service.
3. Converted breach loading muskets sold as surplus by the French (and Germans who captured many) to Belgian firms who reworked them into cheap shotguns. Conversion consisted of shortening the wood and reaming them into shotguns.