Flamer would use no arc otherwise the projectile sprite doesn't show up. Damage radius is for splash damage from a single 'bullet', so with a radius of 0 only the target gets hit (presuming a successful attack) damage radius of 1 then anyone within 1 tile also takes damage. So you can throw a grenade at the ground and anyone within it's damage radius will take damage. You're not taking into account that each projectile must make a chance to hit dice roll, just because they are in the same spread arc and even if you are using duplicates of the same target doesn't mean that they will all get hit all the time. But yeah cone is definitely different from the other arcs. Say you fire a burst of 5 rounds, then you can only hit a maximum of 5 targets with 'burst' or 'spray' but I certainly remember hitting more than that with a burst from the Pancor. Maybe cone multiplies each projectile the further away the target is, but I definitely remember a test firing of a shotgun against a group of closely packed targets and seeing a definite V pattern of those that got hit. With those outside the narrow point of the V (closest to the pc) never taking any damage.