The 300 Dakota has a little more capacity than the 7 Dakota
. Some have done the 7/300 Dakota. It would be equal to or maybe slightly larger than the 7 STW.
My idea for the 7 is a Lapua case. Same as a 7 RUM but better brass and a shorter case. This is only if nitriding proves good for extending barrel life. I'll be finding that out soon.... in the next few months.