It has to be trimmed from .375 Winchester brass. Good luck finding that! Some say you can blow out .30-30 Winchester cases, then trim them down, but then others say the brass will be too thin to be safe. It is not a straight-wall case. You will likely need to order a custom die set.
I was very fortunate because my seller also had some loaded commercial ammo for sale. It was made by a company called Bullseye Ammunition.
If it needs a new barrel or a cylinder, then I hope you know a good machinist.
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