M-4 - Barrel too short for its small bullets to develop the physics to penetrate a car door or kill a human. Gas tube just too short to ever work.
For real 5.56mm rifles (not submachine guns with power robbing stubs), folks who are in the business of killing motherfuckers are snarfing up ammo 65-grains and up, according to Paul Markel.
And you know, if HK didn't think we sucked, I'd be so there saying we need an HK417 (14 inches, .308.)
But screw that. DSA Arms has the beautiful OSW and a dozen other rifles in .308 that can ACTUALLY FOLD SO THEY CAN BE DEPLOYED INSIDE OF VEHICLES!
Collapsing tube stock my fat, pollack ass.