The "Pack-A-Punch" is a machine used in
Zombies in Spaceland to change a weapon's name, attachments, damage output, magazine capacity, and appearance; ultimately transforming the weapon into a better variant.
In order to unlock the Pack-A-Punch you must open all 3 areas (Journey Into Space, Polar Peak & Kepler System), power them, and activate all 4 portals on the level. Once you have done this, you can use the main portal in the middle of the map to gain access to the projection room which has the Pack-A-Punch machine that will accept any gun + $5000 to work.
This will require you to reach at least Scene 8 and spend your money wisely; and can be done solo or in a team. The teleport locations as well as more details can be seen in the video.
[0:04] - Journey Into Space
[1:00] - Journey Into Space
[1:33] - Polar Peak
[2:38] - Kepler System
[3:05] - Projection Room / Pack-A-Punch Machine