For the most part I use the same caliber case as what bullets I am cutting out with some exceptions. I use a 357 case for 358, 359 and 360. Like in the pic I cut bullets for a 358 Winchester (sized at .360) with a cutter made from a 357 case. For all my 30 caliber I use a 7.62X39 case. For all the 44s I use a 44 mag case and so on. Cutting a 44 with a 45 would not make a clean enough cut for me although I admit I have not tried it.
I just use a fire formed case in the somewhat correct caliber. Drill the primer pocket out and insert and framing nail with the head towards the bullet. But that is just me there are lots of ways to accomplish cutting the bullets out.