A gameplay mechanic in Call of Duty: Black Ops Zombies. It allows you to upgrade your weapon. Usually costs 5000 credits. To purchase upgraded ammo costs 4500 credits, or you could wait to get a max ammo. Upgrading weapons is costly but worth it. Upgrades damage by at least 125% and gives a new camo to the weapon and a random attachment.
I put my M1911 in the Pack a Punch machine, and I got Mustang and Sally, the semi-auto, akimbo grenade launcher pistols