imported post
Firearms not suitable for sporting purposes "... any centerfire firearm with a protruding pistol grip, an internal magazine capacity of 5 or more rounds, a barrel length of less than 20 inches, the capacity to accept a detachable high-capacity feeding device, any military caliber, bayonet lug or flash-hider, any 'shoulder thing that goes up', any firearm capable of being fired with a Pistol Grip Only, or any combination of the above parts."
Firearms not conductive to micro-stamping trace methods "... any firearm that retains cartridge casings after discharge, i.e. all revolvers or shotguns without ejectors, any firearm, to include either breech or muzzle loaded blackpowder firearms, that does not use a steel, brass, or other deformable metal casing to hold propellent."
Firearms not conductive to micro-stapming trace methods "... any firearm that does not engrave a microstamped serial number on any projectile fired by such weapon, i.e. any smoothbore shotgun."
Firearms that resemble any current or former military arm "... any firearm that resembles in outward appearance, regardless of caliber, any firearm used by a modern army after 1860."
Firearms or Destructive Devices " ... any firearm with a bore of more than .50 inch except for that which the Secretary of the Treasury has determined is suitable for sporting purposes."
"Machine guns" "... any firearm capable of accepting a detachable magazine of more than 12 rounds.
Handgun not suitable for sporting purposes (aka those evil TEC-9's and things like that)... "any firearm of any caliber with either the clip, magazine, or other ammunition holding device situated in front of the trigger, any handgun that is chambered in a caliber either in current use, or in former use by any military or government agency."
Saturday Night Specials "any firearm lighter than xx-ounces, or constructed of a material that deforms at less than xxx-degrees temperature, any firearm manufactured with any easily removable or easily defaced serial number plate. Any firearm less than 8 3/4 inches barrel lenght."
Dirty Harry Specials "Any firearm heavier than xx-ounces, or with a barrel of more than 4.5 inches"
Sniper Rifles "Any centerfire rifle capable of using a telescopic sight of more than 3-power or any rifle capable of firing more than 500 yards"
I did the above on a spur of the moment. You can do anything, if you only phrase it correctly.