In a legal sense any prosecutor that tried to argue that ammo as more deadly would be the one that looks like a nut. You can say "its no different that the regular stuff and since I make my living from work and not stealing I had to actually buy it and it was cheaper, and it's just a joke". All in all it's just packaging.
I think that if you were really facing zombies who are already dead, the only way to stop them would be to totally disable them so they couldn't physically do anything to you, so anything less than a shotgun would be futile because you would have to dismember them.
Anyways, I don't worry about a coming of a zombie appocolypse, I worry about the ********* appocolypse that is already upon us.