When it comes to grenades, I am thinking micro-grenades, the ones that can be used to blow a hole in doors, or have a 5-feet blast radius. Or maybe, this is a multi-round gun which can shoot high-calibre rounds that can punch through a hole in engines or a tanks. And when you need shotguns, you just change the bullets. So, this is a short-range weapon, (10-35 feet) and is only a backup weapon. Yeah, this can work.
Now help me choose, which one looks nice/functional because I am going to paint it black:

As a shotgun, this scope is ideal. And as a
grenade launcher, this scope is still OK.

So, with a 'laser' aiming system, long range
targets would be easy picking.

Well, this scope is nice, without you having
to explain, everyone can see that it can fire
at long range targets. But isn't it a bit too
bulky?