The increased damage against undead on the Deadshot armor set has no relation to guns despite being part of an alchemy path based around being a gunner.
I would rather have gun CTR medium on both the Deadshot Chapeau and Deadshot Mantle. It would allow for more variety while still following the theme.
I agree that the dmg undead doesn't make sense but if the bonus was switched to ctr med i dont anybody would want to use it anymore seeing as the charge for most guns kinda sucks