I haven't used them, but there is a "button" on the bottom of the can that when pushed breaks a seal on a chamber inside the can releasing part 2 of the paint into the part 1 of the paint. So the whole can is now activated, just as it would be in a conventional gun. I have never been sold on the idea that you can get as good of paint out of a spray bomb as you can from a gun. It's usually lots thinner so it can be pushed out of that small nozzle.