Why a pump? Given the amount of shot going downrange from one or two rounds AND the impact on your shoulder AND the expense of each round, a double barrel is more than adequate. Besides, you'll need the weight of the extra barrel to deal with the recoil which, take it from someone who has a SxS 10 gauge, is no worse than a 30-06 (though the gun is HEAVY - as in 10 lbs!
The 10gauge also patterns much better than a 3 1/2" 12 gauge since the shot is not strung out so far and since less of it contacted the bore on the way out and thus is less deformed.
Now if we could find a source for reasonably priced 10 gauge ammo...