Just so it's on the record: I've been fiddling with making Shotguns that shoot projectile type Fire, and it's not possible as of 0.9.9.3a to make a shotgun that doesn't
A) Use Shells and Shrapnel damage
B) Use a cone type (Normal, Double, Assault are the cone types - Double has wider spread but sharper dropoff, while assault has narrower spread but less dramatic dropoff)
By comparison, hacking a pistol can give you a rocket launcher that wipes out the screen, a BFG that only uses one ammo, a chaingun that effectively fires rockets, or a plasma rifle that only shoots one 10mm bullet. I still haven't figured out how to make them load different types of ammunition.
In short: On an AoSh game, the Carnage Shotgun would still be a P-Class weapon, and therefore disallowed.