Hi Stephen, the Ruger PC Carbines will have a 16.12 inch barrel Sir. This gives them a non NFA requirement and are legal without any special paperwork. Cheers and stay safe!

As mentioned below, anything less Than a 16" barrel turns it into an SBR (Short Barreled Rifle) and would need an NFA Tax stamp at $200. That also depends on if your state allows one to own an SBR.

Stephen, legal barrel length for a carbine or any rifle is 16 inches. If it has a barrel less than 16 inches it would be considered a short barreled rifle/sbr and require a $200 tax stamp. You can do something like a 14.5 inch barrel and permanently attach a 1.5+ inch muzzle brake by pin and welding it and legally that makes the barrel 16 inches since it's permanent but that's about the shortest you can go and still legally be considered a rifle/carbine. Hope this helps.

Stephen, the barrel must be at least 16" or it will considered a short barreled rifle. The rule for PC carbines is the same as any other rifle. Have a great day!