Fuck me, ruskie bro, you've been busy in my absense.
If you can make the bullet diameter .308, you can make the cartridge accept a great variety of 30 caliber bullets as it is, and make the standard an aerodynamic 115 grain bullet sitting on top of a quantity of w296 powder to give .357 power from it with much better ballistics. The addition of a bottleneck means the feeding is going to be more reliable too given the correct neck angle- 40 degrees is sufficient. Given a .308 die set that I am going to buy soon enough and a 10mm case from somewhere, this is probably doable as a demonstration of the cartridge.