well, not enough gas getting to the gun will do this. if it multi fires then the bolt may not be clean, not sure on the water bit....dont tend to get my marker wet
that bit is called the bolt pin, when u pull it out, theoretically the bolt should come out the back so you can clean it!
i work with infernos, if the bolt doesnt manage to re cock, generally its cos its running low on gas, cant think of any other reasons