If you do you will destroy a perfectly good rifle. The Whisper is designed to shoot Pellets not BB's. It has a rifled barrel (Grooves in the barrel to catch and spin the pellet) this makes them fly straighter. Pellets are a soft material. BB are a hard material. Forcing them through a rifles barrel will destroy the rifling. This is why BB rifles have smooth bore barrels. If you have started to shoot BB then you have already started to destroy the accuracy of the rifle and dropped it's value. So don't do it.
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