Actually, depends on what zombies you speak of, here in Mass the police are all moving to .40 S&W cartridges, so that’s also going to be plentiful.
Know your prey. If Govt zombies are your infestation problem I would still stay with 9mm and 5.56mm, reason being that the first line of zombies carrying .40 S&W are limited in numbers whereas the 5.56mm come in greater quantities. Also, if you win your first encounter, you would have a .40 S&W as a backup. If you loose your first encounter, then the question is moot.
All of my guns and ammo were lost in that awful fire...the day after Hussein was elected. Naturally I haven’t replenished my supplies as we now have a post-racial, post-political “WUNDERKIND” in the Whitey House. There is no longer any crime, freedom abounds and the M1A1 in my yard is just for show.