A popular co2 pistol out there is the Umarex cp88 competition whichl is semi auto and has a rifled barrel, so does that also makes them illegal?
If so then there are a lot of those around, and I am sure other semi auto co2 pistols have rifled barrels.....
Type:*Pellet air pistol.
Model:*Walther CP88 Competition Matte Black.
Materials:*Mostly metal construction.
Barrel:*5.5 inches, metal rifled.
Propulsion:*CO2 x 1.
Action:*Semi auto, single and double action.
Ammunition Type:*.177 caliber pellets.
Ammunition Capacity:*8 rotary magazine.