Don't know. To my knowledge they are not on anyone's MTOE in the regular army, so they aren't even a concern. I've never read anyone using them beyond Marine testing.
As for the rules. One of the major advantages to shotguns is that you don't have to be a sniper to hit your target. A 2 3/4" .00 buckshot shell contains 9 .33 caliber pellets, a 3" shell contains 12. IMO the rules for medium and wide choke settings reducing defense rolls is somewhat fair. You could houserule that you get a bonus to dice instead.
