The 8 holes in the side of the gun correspond to the 8 lego technic axles that are inserted into said holes in order to install the cartridges.
Each cartridge has 4 holes in it, allowing 2 to be in the gun at once.
The trigger can move back and forth.
The top of the Hypertrig is held in place by 4 of these red technic pins; two on the front, and two on the back.
The ones on the front are hidden behind the front part of the barrel, which can be taken off.
The lower half of the Hypertrig can have two cartridges put in it,
and the top half of the Hypertrig has a tool in it that makes it easier to remove the pins that hold the cartridges in place.