
This card is disappointing. You are spending an additional 3 XP, and you are getting nothing but -1 cost and a difficult to use limited special ability.
First, fighting more than one enemy at once is something that happens, but it is a lot less common than fighting one opponent. Two, even if you are fighting two opponents, you probably have to hit by quite a lot to activate the power, it isn't that easy to do, you’d better be pretty great at fighting. Three, even when you get into the magic situation and it works, it still costs ammo, so all you are saving is an action. And other cards which give “two actions for the price of one” have the advantage that you only have to spend your boost cards on one action instead of two. but in this case, you have to hit by so much to trigger the special power, that it probably would require fewer boost cards to hit twice normally then to make the one really good hit that activates the power, so really, you aren't gaining much other than saving an action.
Now, it is true that saving an action in combat is a particularly good time to save an action, but this card just places too many limitations on that saved action. As an upgrade, compare it to .41 Derringer (2), which has a much easier to activate general purpose way to give you an extra action, and gives you an increased hit bonus. This upgrade costs more XP and does a lot less.