Flares should not be used in shotguns, unless said flare specifically states it can be used in a shotgun. The 12 guage flares made by Orion for marine use do not fall under that. Want redundancy? Buy another flare gun. They sell them at Walmart...
On the flipside, don't be stupid and try to fire a 12 gauge shell from a flare pistol. Not only should it not chamber due to design, but if you manage to fire it, congratulations, you will have created a hand grenade
The pistol is made out of plastic or weak metal.
There are also hand held flares and smoke sticks if you want those, too.
You can also buy stand alone or under barrel mounted 37mm flare launchers, too, and have some fun with those.