the valve is steel. the hammer is steel. the mushroom head on the valve stem is synthetic (delrin ?), encased in brass. the (inner) valve face is steel.

so the only way it cannot fire is if the valve stem delrin mushroom is not being knocked away from the sealing face of the valve. generally, the only things that hold it in place are air pressure (hence you pressure lock situation) and the valve return spring.

this is why I suggested the power adjuster (which limits and can block) valve stem travel be checked first.