When Pack-a-Punched via the Pack-a-Punch Machine, it becomes the Porter's Mark II Ray Gun. When Pack-a-Punched, the magazine size doubles, the ammunition total increases and it fires red rays instead of green. A player cannot carry the Ray Gun Mark II and the original Ray Gun at the same time; if the player has the original Ray Gun, it is impossible for them to receive the Ray Gun Mark II from the box, and vice versa.
In Patch 1.12, the Ray Gun Mark II was unintentionally added to all maps (several days prior to Vengeance's release for Xbox 360), but was later removed swiftly via a hotfix.
In first-person, the weapon is held like a submachine gun, but in third-person, it is held like a pistol.
Because of the different type of rounds used, no splash damage is made by the impacting of the gun's blasts. The Ray Gun Mark II's shots can also penetrate through multiple zombies at once, whereas the original Ray Gun's shots stop upon contact.
While its predecessor is reloaded from the front of the weapon, the Ray Gun Mark II is reloaded from the back. They both use the same "cold cell" ammunition, however.