where's the Part in the pen gun where the compressed air gets accumulated to push the projectile out

Jimmiy101 ,lets say i have a blower gun like this ,now where am i going to drill?
Jakethebeast can you attach a picture of the Y-shaped connector ?

you can get these kind of piston seals from some shop which sell ball bearings and similar stuff like that

I consulted with a member of this forum Wyz2285 and he said i need to replace the air blower gun with some other thing to Increase the power i have no idea what to use instead of the air blower gun and maintain the shape of the Grip (I've considered using PVC ball valve but the problem was it wouldn...