I was fooling around in Slab6, making a new gun because i was bored and i ended up making this
It is not based on any other weapon or anything, but i did had the bulky design of the C-14 Gauss rifle in mind (the rifle the Marines in Starcraft use)
This is the outcome:
Download: http://www.mediafire.com/?gzr78eaeqeebj8d
In-game in your hand:

In-game held by other player:

How it looks like in Slab6:

How it looks like in Slab6 with toggled Normal Shading and Face Shading:

In my opinion i think i can replace all guns, semi, smg, and even the shotgun
Just rename the filename and replace whatever weapon you wish to use