Laws and restrictions here vary. Some states there are no regulations at all, others classify air guns right along with firearms. Power wise they are comparable to blackpowder arms and in that same vane use lead projectiles with out jackets, Cast bullets in other words. Beauty is no propellant fouling of the bore. The compressed air has been contained in many different fashions tube under barrel, or a bottle in same location, Butt stock reservoirs, and others. Some units require pumping per shot some are hybrids. Big bore air rifles have been around since the beginning of fire arms, and in some cases were better than their explosive counter parts. Here in the US we are just way behind. Napoleon army in countered snipers armed with air guns, Standing orders were if any opposing force was caught with an air rifle they executed on the spot. There was an entire company armed with them I forget the details at present. Air canes were a popular defense weapon. Lewis and Clarke had one on their expedition. Air powered weapons have a history as long or perhaps longer than firearms. These are not the Daisy Red Riders of your youth. The air pressure contained in these units ranges from 2000psi to 4300 psi in the case of pre-compressed units ( PCP).