Or they could just do it in 4.6. I don't think anybody would mind. Hell, I already stock 5.7mm, but wouldn't mind another.Here is an idea. How about instead of a 22 version of the MP7, a 5.7 X 28mm? I think it would be closer to the 4.6 caliber.
The 5.7 is a fun round to shoot as well.
Also, 9mm USC parts would be the best. I'd prefer a 9mm to my current .45, since I have almost all 9mm pistols. I'd assume 9mm USCs would equal 9mm barrels and bolts, so yeah.