A little help please. My grandson got a 760 pumpmaster pellet gun for his birthday (from Walmart). It has yet to fire its first shot. Maximum pumps reccomended is 10. But it builds up no pressure. I tried lubricating it for him, but same results. Not exactly a gunsmithing problem I know. Any ideas? Walmart says you bought it, you own it. Refuse to exchange or return it. PS, dont get into an argument with store management while you are holding a gun.