A lot of people think that a BB is harmless, Some of the guns use a CO2 cartrige, others are pumped. We used too use them for target practice. WE had a 2x4 back stop and found that we culd pumpp the gun enough to penitrate a half inch into the 2x4s.
A sujestion is if you find someone using a BB or pelt gun call the police and tell then that a gun is being fired, do not say what type of gun!
They will be there fast.