[Christopher R. Rice]

I'll add in addition to Bestows a Bonus being the way you add bonus or to hit rolls to damage, adding Enhancements simply treats the damage dealt as the "basic damage" of the attack and adds to that normally.

So if you did 3d large piecing damage with a pistol and you wanted to add Incendiary to the weapon's damage it would be a Lesser Transform Matter effect plus +2 energy. See p. 5 of How to Be a GURPS GM: Ritual Path Magic for more info on this.