This is one of many questions whose answer is " it depends on who you ask". I can understand how too light a pellet could and probably will damage a springer. I've never read adequate explanation of how shooting a "heavy" pellet could hurt a spring gun. I think us "amatuers" are supposed to defer to the opinions -and ultimately thats what they are-of the "experts". After buying my first spring -piston rifle and reading here how a " heavy" (define heavy ) pellet could damage my gun, I asked a well know expert if shooting an 11-12 grain pellet in this .177 cal rifle was ok, he said "if it's the most accurate, go ahead and shoot it." I figured he should know, as I bought the rifle from him.