Well, the idea is to have a projectile that is useful to longer ranges than, say, ordinary buck shot. The thought being.. if you could just get a slug accurate and powerful enough to be a one-shot stop at 100 yds, then you'd have a gun that dominates the 0-50yd range (buckshot) and is servicable out to 100 yds with slugs. A formidable weapon.
The idea is not to be able to shoot out to 600 or 700 yds like a .308. The idea is to extend the useful range of a shotgun beyond CQB.
And please show me a reference for a sub-MOA FAL. A built rifle for sale would be great.. but even just a smit