progear black gearbox "systema inside" m140

[BigZee87]

Hello all,

Had anyone used one of these before? I have had a response to a wanted add for a v2 box with a bran new one. Asking price is 70 but think I can get him down a bit.

By the looks of it its a reinforced box with systema helical gears an m140 spring and a bore up cylinder and piston that will put out about 450 fps.

Question is how good are these? Are they strong? Do they last and what will happen if I put an m100 in and will the cylinder still work in a carbine length gun?