Qual-Cartridge makes properly headstamped 400 Whelen brass.
To fire form, you put in a full load for a 300 gr bullet, seat a jacketed 41 S&W revolver bullet BACKWARDS so that it bites into the lands. Bolt should take some effort to close.
BANG and you'll have a case exactly fitted to your chamber.
Then send the cases (3) to Redding and have them make you a neck sizing die. You'll be set for life.
It's also a great gopher load out to 50 yards or so.
