Im new to all this - this will be my first post. So excuse noob questions. I have had a look around first, to get some ideas, but havent found just what I need yet. Can I explain my plan, and you can all comment on the viability and offer up your thoughts if you are willing? Thanks.
I've been a paintballer for many years, and have made various paintball guns. Im not hopeless at hacking things together.
Im wondering wether I can make a paintball mine, that will fit inside a .556 ammo tin. This is smaller than most of your guns.

I would cut a hole in the side (or bottom ) about 100mm in diameter. Inside I would have a sprinkler valve, a pressure chamber with a gauge, and a paintball fill nipple, and the short wide barrel. This way anybody in the team could fill it from their remote line. Ideally an adjustable purge valve too, to make it safer.
I would use a PIR to detect motion to the front, and fire the solenoid that way. I'd add a safety switch, and allow a one or two minute delay after switching it on to allow the user to clear the area. I'd probably also add a remote firing system. I can do the electronics no problem....dont need help there.
The mine would fire a mass of paintballs poured loose into the wide bore barrel, like a shotgun. Velocity can be lower than you normally get with your spuds! Im aiming for an inaccurate short range shotgun effect.
What Im hoping you can advise about is this:
1) do you know of any examples of this already done?
2) will I be able to fit it all in that can? I hope so - as these need to be carried. Ideally, I'd make 10 so all team members carry one, and we place them around us in a defensive perimeter when we need to.
3) Would an air horn solenoid work instead of a sprinkler valve? (they're smaller, but also much smaller bore which is probably bad)
Thanks very much in advance for any helpful advice and suggestions.