A different approach might be buying a Rossi/BrazTech, I believe they sell Rifle shotgun combos, i think they have a 12 gauge that you can get with additional rifle barrels chambered in the popular hunting callibers, a 12 gauge barrel with an interchangeable.308 barrel under $300, that doesnt sound like to bad a dealto me, again you are stuck with that one shot one kill deal, but i personally love the idea of only one shot, might bot be the best route but at least thought id suggest it,