What American Handgunner article is that???
I did/do have a .256/30 Mauser C96 that I did years ago. Uses the Hornady 60gr JFP #2510 bullet. Clymer ground the reamer. Still have the barreled upper but passed the C96 on. Flat shooting; loud crack.
The barrel was originally much longer but I cut it back and re-chambered it. My cartridges were made from .223 Remington brass cut down and reformed in a .256 Winchester Magnum sizing/reloading die. Chamber cut with a .256 Winchester Magnum chambering finishing reamer.
Bullet, cartridge, comparison of .256 and .30 Mauser barrels, reamer, and barreled receiver. The #2510 bullets still show up on GB and eBay frequently.