I don't know exactly why, but the feds really have a love affair with those 14" barrel 12g Remingtons. They run the guns with regular full size buttstocks so they are still not really all that small. Benelli came out with 14" versions of their shotguns just to compete for the .gov contracts.

Regardless of the law, I pretty much don't want a shotgun with a tube that is much longer or shorter than 20".