I just tried Charles' method on my new Heritage wins, and it worked perfectly. Thanks ! It was much fast than my bolt cutter chip the corners off the slab method, and far safer than my single failed attempt using my radial arm saw several years back. The saw blade grabbed the rubber insert and pulled a nice 1814 into the blade - giving it a shiny new planchet clip.
The hammer has always worked fine for me. I'd thought about using my bandsaw, but usually too lazy to walk out and fire the thing up when I have a hammer in the house.