Why not the right double shotgun with slugs? Last year I saw a 3 1/2 inch mag slug load intended for "dangerous game". I'm assuming a nice and heavy hard slug but didn't look into it any farther-don't need a load that heavy for Iowa whitetails. They were about $30 for a box of 5, but if you're not going to use them outside of a life and death situation why would you need more than 2-3 boxes(one to find out what to expect, the rest in case they're needed). That way, it's still a "double", add rifled choke tubes(my shotgun's only a Stoeger but I'm sure some higher end makers offer doubles that take choke tubes) for a bit of accuracy improvement if desired-probably unnecessary at charging range, but someone might want it for hunting. Buy a double in 3 1/2 inch or if barrel contours allow it ream a 3 inch to 3 1/2, drill and tap the rib and install rifle sights, find out point of aim and it should be ready. I prefer a the right double with double triggers to a single barrel action for survival, easier to switch triggers in an emergency than to switch guns-if a second is available.