I purchased a box of this weird blue plastic ammo for my .308 Ruger American. I believe it is German surplus from the 90s. It shoots a 10 grain plastic projectile at almost 4000 fps. Sounded interesting and only 20 cents per round, so I decided to try it.
I loved shooting the stuff. There's absolutely no recoil, so I can see how I'm jerking the trigger as I'm shooting. I think another couple hundred rounds will really improve my shooting. And it will be my training ammo whenever I teach someone to shoot.
I'm also thinking about using it for small game hunting. I don't own any smaller rifles, so I've sometimes hunted rabbits with my 308. A less powerful round could make things more enjoyable and I always take head shots anyway, so it should be enough power to kill them.