I have 10 of the brass "cartridges" for mine and I've never used them. I bought them from Buffalo Arms thinking they would make life easier. Unfortunately they don't fit my gun. Maybe it's because of the Hahn modification, but they are too big and won't fit. I'm actually glad, because making paper cartridges is half the fun of having a Paper Cutter. At least for me.
But it was an expensive lesson. Now I have 10 cartridges that I'll never use.