An air gun is classified as a firearm only when over 500 fps and over 5.7 joules, has to be both.
http://www.rcmp-grc.gc.ca/cfp-pcaf/fs-fd/air_gun-arme_air-eng.htm
Correct me if I am wrong but that would mean a steel bb weighing in around 5.1 grains can exceed 500 fps just as long as it doesn't exceed the energy level of 5.7 Joules. According to my calculation a standard .177 cal BB gun can shoot a BB up to 612 fps before it would be considered a firearm that requires licensing of some sort.




















































