I think you would be wise to look it up. As Old Ugly Guy said, regulations can vary a lot from state to state. Some specify minimum caliber, some minimum projectile weight or powder charge, minimum barrel length, or some combination of the above, and possibly some parameters I haven't even considered.
Regarding barrel length, I understand that some states that have policy makers more accustomed to dealing with breech loaders measure barrel length as bore length, meaning from the muzzle to face of the breech plug (or bolt, in a breech-loader). This is how barrel length is measured in most breech-loaders (except revolvers, which are measured inside the bore from muzzle to cylinder face). This means if the threaded shank of the breech plug in your 12" barrel is 1/2" long, your bore depth will be only 11-1/2", and if your state law requires a 12" barrel, you may be out of compliance.
One more way for them to get you. Watch out!
Notchy Bob