yep 100% legal to own one, the law only prohibits them if they shoot above 330fps then they become firearms and as such are a prohibited weapon, requiring a license.
well i think i see where you are going with 'other means' but you can use it for whatever you dam well please so long as it does not cause any damage to person/property or any other common sense stuff as this obviously comes under crimes such as aggrivated assault, vandalism etc.
i really hope you aren't going to say 'rob a supermarket' but what other means are you thinking of?