Empty Quiver Style + Leaping Shot Deed + Whirlwind Attack
Notice as Whirlwind Attack says "When you use a full-attack action" and Leaping Shot Deed says "As a full-round action", and of course Empty Quiver Style saying "You can switch between melee and ranged attacks with this weapon without penalty, even during the same round." ...So, does that mean that I can use my firearms as a light mace while moving with Leaping Shot Deed and making Whirlwind Attack?
And another theory I have that extends this is: what if attacking with a rapier while just holding a pistol in the off-hand?
A full-attack is an action type of a full-round action.
Leaping Shot is its own full-round action, and therefore is not a full-attack action. C.f. running is a full-round action too, but is not a full-attack action, because it is its own thing.
You know, since Whirlwind Attack says it doesn't add any bonus from other feats, I think I made a mistake in this theory.