In my quest to put an underbarrel pump shotgun on a battle rifle, I figured I'd ask if anyone could identify the shortest, lightest model out there. My first guess would be Mossberg 500, which I have in 26" barrel (would get an 18" barrel). But are there others that are even lighter and have a shorter action? Here's another issue: For a non NFA shotgun, the barrel must be at least 18" and total length 26". Now if the shotgun is not set up to be fired apart from the rifle, would the rest of the rifle count towards the total length, which would be well over 26" (try double that)? That could save a bit of hassle.