If it has an insert that has a lip on the inside to keep you from inserting a regular 12 ha. shot gun shell then it was professionally made. If there is no lip then it's after market. Either way it will work with 12 ga. flare. If it's smooth it will also shoot shotgun rounds. Two issues exist. One, will it explode under the pressure generated by a shot gun shell. Two, do you want to risk jail? You would essentially have a sawed off shot gun on board. There are a bunch of the inserts out there but everyone would have to deside for themselves if they want one on board. "Machete Stopper" is the name they were called and you could buy them on the internet.