Titan Sniper Rifle: Sniper Gun Variation

I wanted to design a Sniper Rifle. I thought it'll be cool to have different color variations!
I got inspired from playing video games like Halo and Mass Effect. I wanted to make the guns look futuristic. I did most of the design from memory and several references.
On the other hand, I've never held a gun before, only seen it on movies, shows and games. I would greatly appreciate it if you leaving critiques, so i can improve for future weapon designs.

I recently fixed and made the barrel slightly thicker as i possibly can!

Concept Art: Titan Sniper Rifle
Designed and Painted on Photoshop CS5!
11"x14"