use two of the same model with the same bullets and do a double tap to the back of your head

What if you don't hold it normally? Use a type of ammo from a weapon normally too long for suicide and connect something to the trigger so you can reach it, or wrap the balloons string around it.

If you watch enough true crime you can probably work out how to make your suicide look like a murder, or at the very least leave them confused for a while.

Ghouls. Missing items at crime or accident scenes happens. People come across the scene and help themselves.