Any length will do it will become an 18.5" barrel no matter what. Doesn't have to be perfect but does need to be serviceable. If you have a take off stuck in the closet somewhere or maybe a barrel with a frozen up choke you don't want to mess with let me know how much you want for it. I may be interested in a blackhawk knoxx specops stock. Just playing around with a toy for the sake of playing.