The EXO ONE (X01) is pretty slick. It takes advantage of the SIG P320 Fire Control Unit (FCU) as a plug-and-play component. This multi-caliber exoskeleton accepts the FCU, barrel, slide assembly, and magazine release and can be configured in 9x19mm Parabellum, .357 SIG, and .40 S&W by transplanting the corresponding P320 components (.45 ACP is in development, as the changes in magazine well dimensions require a specialized lower receiver).
It features a non-reciprocating charging handle locks the action open (the slide to the rear) with an upward motion when fully retracted. The action can then be released with a downward motion (akin to HK-style weapon systems). In addition, if the charging handle is in the forward position, the slide can be released via the FCU slide release during reload procedures. The X01 features three M-Lok slots near the muzzle for accessory and grip attachments. The upper receiver features a 19-slot milspec M1913 picatinny rail.
Like the SIG MCX and MPX, the rear of the lower receiver features a vertical M1913 Picatinny rail to accept SIG MPX/MCX buttstocks and arm braces.
