One rifle to rule them all...

[20X11]

Home defense and elk hunting seem mutually exclusive....that being said, inside 200 yards on elk, home defense/SHTF, fun time at range, it would be hard to beat the .300 blackout. Brass is easily made from 5.56/223 cases, New plinking ammo is relatively cheap, you can put a can on it and run subsonic loads for home defense, and get 150gr 30 cal bullets going 2000 fps for elk. And since it uses all the same parts as a 5.56 AR except the barrel, parts are cheap and readily available. Plus the effective range (as rated by the military) is 440 meters...which meets your 400-500 yard requirement.