thats a headstamp from Dominion Cartridge Co. in Canada
it's .032 shorter than the .357 maxim, was used in the Winchester 07 autoloading rifle. Used a 180 gr bullet at around 1850 fps.
case length-1.380
case mouth- .377
case head width-.410
rim thickness- .050
inside diameter of the case at the base...just above the flashhole- .381

http://www.ammo-one.com/351WSL.html