The gun nightmare is officially over for Buffalo Bills lineman Adolphus Washington -- who was found not guilty of improperly carrying a concealed handgun stemming from a incident at a water park. 

As we previously reported, cops drew their weapons and stormed Washington's car when they saw him handling his gun while leaving a party at the Cincinnati-area waterpark on July 9. 

Washington claimed he was innocently trying to put the gun away -- and wasn't trying to brandish it. 

He was arrested and charged -- and Monday, the case went to a non-jury trial where he was found NOT GUILTY. 

He's off the hook with the law -- but could still face discipline from the NFL.