When drawing guns, it also helps to learn a bit about the mechanics, to make them appear as if they could actually work.

Thanks for the advice. Do you think I could learn a bit about gun mechanics if I took one apart myself?

I don't know, it might be safer to look it up.
For example, the inside workings of a gas blowback mechanism:

You can see that the round is taken from the magazine into the barrel, by the bolt moving forward, when the trigger is pulled the hammer is released and hits the pin forward through the bolt. The pin then hits the primer, thus firing the bullet from the casing. As the bullet goes down the barrel the pressure behind it goes up into the gas block (the tube above the barrel) and pushes the bolt back to load another round.

Well it goes something like that.

I made it look a bit better, but I'm a bit frustrated with my drawing incompatibilities.

I think I'm lacking a good drawing technique. I can draw most things easily, but some things, like heads, helmets, guns, and wrists/hands feel a bit unnatural, and I when I sketch, I tend to miss details.

The problem there is that you coloured with a floodfill on the same layer as your lines, so you get nasty fringes.
Also you'd get a good idea of how a gun works if you took it apart, but you'd only really get the drawing benefit if you drew it at various points and took proper notes.
Regardless, the only way to improve drawing technique is to do studies (or at least draw a heck of a lot)

Isn't he wielding a lasgun? Because then gun-studies wouldn't really work.
Anyway, the drawing looks pretty good, maybe a bit dark but that's just my taste....

He may be. But to me there seems to be an ejection port and a magazine.

I use the white lines as an outline, and I color over them as I go along. I fixed the gun up a bit, it looks more like a las-rifle.

I'm really unsure how to color the gun, because it is outlined in black, and guns are usually black...

Maybe a nice silver color would go well with the blue. White is probably too bright to fit in with the rest of the scene, seeing as the actual character pictured there is totally black.

if that's supposed to be a soldier then I need to point out the anachronism dramatically more important than gun design: a soldier wearing a ♥♥♥♥ cape

Is it a cape? It looks like a waistcape, like an open fronted kilt with pants under it. Maybe it's just tied at the waist.

it's enough of a cape to be completely and utterly impractical

although I suppose it could be a dress uniform? sure, that sounds plausibleish

I'm sure this isn't plausible at all.
http://en.wikipedia.org/wiki/Greatcoat
Nope.
Not even a little bit.

in order:

russians, who live in COLDASSCLIMATE which invalidates all other considerations on clothing
dress uniforms
non-combat troops

greatcoats are only a practical piece of equipment if you're fighting the cold more than the enemy and need to insulate your troops the cheapest way possible

but yeah actually alright that's a pretty good point

I'm glad we agree.
Also, they're potentially useful against shrapnel and and spall, so not entirely impractical outside of keeping out the cold.