Nah, not enough ammo, and you don't really want the zombies to ever get that close to you. If they are close enough to get shredded by that you are already in trouble.
M4A1 with extended clips and a decent scope is the way to go in case of zombies. Keep 'em at a distance.
As for my vehicle safety, I just drive a car so old and beat that no self-respecting carjacker would even think of taking it. "Dude look at this '91 Geo I stole!" Yeah, that'll go over well!