I had the exact same thing. T-hum ( creator of the cradle parts), made me aware of the ice that builds up during full auto shooting. It causes exactly what you say, jamming up the piston. Apparently they use a new "x-ring" that helps this, but im still waiting over two months for mine
.... In the meantime, ask Amos about the RA tech upgrades... He seems to think they might show some promise.