I have a problem and need advise- I have a new Umarex Gauntlet 2 SL .30 cal. , it will not take air- I took the tank of and checked all the fittings they are tight, the tank will fill when its not on the rifle, but when I screw the tank back into the gun it leaks air out the end of the barrel, it will not fill with tank on gun, could someone please help with what might be the problem.