In particular, some air guns that are commonly called air soft guns may fall into this category. These are devices that have a low muzzle velocity and muzzle energy, and that usually discharge projectiles made out of a substance such as plastic or wax rather than metal or lead.
That one word is what saves our asses. Guns will be assessed on a case-by-case basis when the need arises. Till then (until someone does something stupid), the majority of law enforcement won't mess with airsoft users / owners.