yeah they're the king arms ones
I got sick of having to rebuild them every 10 shots, luckily they DO sell rebuild kits but it sucks.
Either the valves leak, the piston's O-ring cracks, or the piston seat gets damaged when reloading. So I've got a few that I've turned on the lathe to get perfect.
Anyway I'm retooling them all to hold bear bangers, and remodeling my M203 to have a firing pin.