I agree with SleepyHe4d in that more thought should be put into the designs based no how guns work since these look like they are based more on realism. You don't have to entirely base what you have on existing designs, but there is reason to why guns are shaped the way they are. For example, the clip is curved forward because the bullets are arranged in them. While it's possible to have a clip that is curved backwards, it would mean the bullet itself is larger than the casing, and the barrel of the gun should reflect that by being bigger as well.
The first design reminds me of a modified AK or something. For a combination MG/Shotgun, it seems to be lacking the shotgun portion. (EDIT: I think I see the shotgun portion now) Adding a second barrel to it will help, and you could probably go with some kind of sawed-off shotgun look and position the barrel where a grenade launcher would go, as long as you leave some concession for shell loading or a clip of some sort. The grip looks workable, but uncomfortable (but not like UT weapons look any better in that department lol). However, as I mentioned about the way the characters hold the weapons, the forward grip should be of the horizontal variety, otherwise the vertical-style grip might protrude through their hands as they hold it.
The 2nd design reminds me of the P90 (my favorite SMG ^^). The P90 has a really unorthodox design in that the clip stores the bullets in a clip that runs along the gun's length, and are perpendicular to the gun. A mechanism twists the bullet into the correct position as they are loaded into the barrel for firing, otherwise the gun looks like some kind of fantasy weapon. The grips on it somewhat resemble the one on your second design, but where the trigger is positioned on it is really where your thumb should be were you to hold it like a P90. If you added a thumbhole behind the trigger, it could work, but like the first design it might look kind of strange when the characters hold them in UT.
I gotta be somewhere soon, but when I get back I'll try and draw up some examples. I think you could make what you have work, they just need some tweaking.