"The greatest evils of the world will not be carried out by men with guns, but by men in suits sitting behind desks. " - C.S. Lewis
The 7.62x25 in an M1 is a great idea.
But how about a clone of the PPSh-41??? It would be a historically accurate choice in that caliber.
Ppsh has been at the lab for a while, not sure if we ever did get the results.