Originally Posted by g.willikers
Your stated use suggests something like what the 3 gun folks use.
Check that out at places like 3gunnation.com and the multi gun section of brainenos.com for ideas.
It looks like suitable versions of the AR are priced in the $1200 to $1500 range.
I would not recommend much at all from my 3 gun rifle for the OP's given purpose...
The 18" barrel is longer than I would recommend, the OP should go with a 16". That also means that he should get a mid-length gas system instead of a rifle length like my competition rifle. Instead of a light 3 lb trigger, a 5+ lb trigger is my recommendation. And instead of a compensator that will make the muzzle blast even worse, a good flash hider is a decent choice. I would also recommend an Aimpoint red dot sight instead of a 1-4x optic for a defensive rifle, but the 1-4x can be used at 1 power almost as well.