Junk Jet and Rock-it Launcher are weapons that fire any junk item loaded into it. This means that wrenches, scissors, teddy bears, and yes even Pre-War money can be weaponized.
While the hilarity of the Junk Jet can give you boundless fun with what to launch at enemies, or citizens of Diamond City like in the video, you need to consider what you are wasting. When you reload the Junk Jet, you are brought to your menu to choose what type of junk you want to use. Do not launch anything that is worth its weight in scraps.
Surprisingly enough, Redditors have found that using the money as ammo is pretty effective.
It is even possible that when you add the Ignition Module to your Junk Jet that you can set that stacks of Pre-War money ablaze as they shoot out.
However, at 8 caps a clip, you will literally be throwing money out a window.