Not the M203 part.
The M203 is an M16 with a grenade launcher slung under it.
[link|http://www.hqmc.usmc.mil/factfile.nsf/7e931335d515626a8525628100676e0c/d50a120f00de543d8525627b006b1fec?OpenDocument|Here]
The grenades need to spin three times in order to arm themselves. I don't know how far that is when launched, but grenades aren't very good choices for close combat anyway. I left "grenade" off of my original list. We had grenade pieces flying over the concrete barricade (figure a distance of 90 meters) when we were tossing them. Being in the same room complex when a grenade went off would probably negatively affect your hearing for a while. Not a good thing when you have bad guys near you.
But, you can put these through windows very easily.
RPG's are more powerful. An M203 would not stop a tank. An RPG can. An RPG is similar to the old bazooka or current LAW.