An unloaded BB gun is no more a weapon than the pop guns that are sold outside of Pirates of the Carribean. Most of the kids where I live see them as toys, and probably would not think they were bringing a weapon to school and violating the zero tolerance policy. The boy scouts even teach kids here how to shoot BB guns. In my opinion, the suspension should have been for no more than five days. Save the real punishment for the violent kids.
Personally, my kids will never own a BB gun, a real gun, or one of the POC guns.