I
f you've ever used or toyed with a single-shot flare gun, like the kind made by Orion for marine signaling use, you may have noticed that the base and primer on a flare cartridge look exactly the same as the base of a 12 gauge shotgun shell—and that's because they are the same. The hull of the flare is a lot different, however, featuring a long, tapered front that acts as a sort of barrel, directing the flare when fired. The actual projectile never comes in contact with the "barrel" of the launcher, which is partly why the plastic guns can be reused.
As the video above shows, the launcher is designed to seat a tapered flare, and a 2.75" shotgun shell will not seat. However, if you were so inclined, you could get a 1.75" shell, like the Minishells made by Aguila, to fit, letting the gun close.
This is an extraordinarily bad idea and something that is far more likely to seriously damage the person shooting it than anything it might be aimed at.
The launcher is plastic...high impact plastic, but still plastic. A 12 gauge, 2.75" shell generates a maximum chamber pressure of 11,500 psi. You'd basically be firing a shotgun shell by striking the primer outside of a chamber.
With no chamber to direct the explosion and projectile down a barrel, the charge in the shotshell simply goes outward, as explosions tend to do, bursting along the path of least resistance.
In the video, the plastic chamber only creates some additional shrapnel. Amazingly enough, we do see buckshot travel down the barrel of the launcher, but it limply bounces off the target only inches away, and the grip of the launcher remains intact.
So in case the thought ever crossed your mind during a boring few minutes on a fishing boat, no need to wonder anymore.
