Hi m4220,

Page 216 of Speed's 'Original Oberndorf Sporting Rifles" reads "By 1905 Rigby had designed a new .350 rimless cartridge, and some rifles were made up on the step-down receiver ring actions with slanted magazine box, which worked perfectly even with the rimless shells. Later a new Square Bridge action with normal front ring was developed."

I have a photocopy of a photocopy of the original Rigby ledger from J. Roberts & Son showing Rigby originally sold the rifle as a .350 Magnum Mar 23rd, 1910.

I assume the .350 Magnum means the .350 Rigby rimless cartridge, unless Rigby used this designation to mean both the .350 Rigby rimless and the .350 Rigby No 2; otherwise, I'm sure this rifle is one of these step-down receiver ring actions with slanted magazine box chambered in the .350 rimless cartridge.