....wait... I better clarify that. If you handload, which you must do for the .357 Herrett, you can load your cartridges with normal BULLETS used in the .357 magnum.
You can NOT use .357 magnum ammunition (cartridges) in a .357 Herrett..... The Herrett is created by necking up a 30-30, if memory serves, to 35 caliber. I also believe it is a little shorter than a 30-30... I could be wrong on that.. it's been many years since I read up on the Herrett cartridges.

"Progress, far from consisting in change, depends on retentiveness..those who cannot remember the past are condemned to repeat it." Santayana