I have some old metal frames from political signs in the back of the grass by the woods. coroplast with roof flashing on top, then colored packing tape to hold it together. Me and the boys shoot them with BB or Airsoft. Airsoft allows you to shoot alot including full auto. I sort of prefer the BB though cause you actually aim it. The airsoft we have is not expensive, I think $100. We shoot the biodegradable heavier airsoft BBs from Dicks. The lighter weight Airsoft BBs are not as accurate it seems. If I only have 15 minutes, jumping into the back yards and plinking those spinning targets is a fun. The kids were hot into Airsoft the end of last summer then went cold on it. the first one was a plastic gear crossman pulse That was single shot spring loaded and electric and it lasted 2 weeks before the motor broke. I got another one that was better and had more capacity but electric only. Crossman sent me a brand new one and it's still in the box unopened.
Airsoft can be fun but if you actually want to use something as a trainer and learn how to shoot a pellet gun would be much better.Most pellet guns (not bb) are just as accurate as a .22, they just dont have the range. I learned to shoot with a crosman 1377 pellet pistol and a rws 34 break action rifle.