Requirements for Replacement of Currently Issued 5.56 M-855 and 7.62 M-80.

[Tony Williams]

A cartridge like the 6.5X25 CBJ in a small family of weapons, e. g., a pistol of near-classic appearance, an 8" barrel weapon collapsible to an 8" X 12" X 1.5" package, and a folding-stock carbine could be of significant interest to these folks.

I had the same thought with respect to the cartridge, but IMO you could replace all three of your suggested guns with the B&T MP9 shown below. It's good for 200m, very light and compact and a real honey to shoot, being very controllable in full auto: