Rob Curtis got the scoop on a new SIG Personal Defense Weapon. The SIG MCX, as Rob speculated it will be named, is the big brother to their recently launched SIG MPX pistol-caliber carbines. Internally all we know is that it uses a AR-15 style rotating bolt and a short-stroke piston. The upper will be compatible with AR-15 lower receivers. Externally we can see that it is integrally suppressed and does not have a buffer tube.