ok i just bought a .177 cal. air rifle for squirrel hunting it was the crossman STORM XT (gets 1,000 fps.)and it came with a center point 3-9X32 scope and i put the scope on the rifle and sighted it in and it seem that the scope is moving and wont hold a zero but its not move from shot to shot i can take 3 shot at 50 yards and have a 1" group but the next day take it out and it will be 2-3 inches off but still a 1" group the scopesaid it was desined for 1,000 fps. are rifles sois this a problem with the scope or gun?