Looks like you have a good workflow going, guns are pretty neat and the polycounts are getting more and more optimized. I'd say keep an eye on those cylinders as I think that's your main polycount drag, it's amazing how many polygons a gun can accumulate if your not careful huh!. The other thing I'd say is to consider animation when making these, the more functional and realistic the gun is, the better. Even Half Life had some neat details, like the ring pull on the grenade bobbing about, so think about what the gun does when you fire it and reload it. YouTube should be a decent resource for this stuff, but things like how bullets eject and how to reload are best researched before the first polygon goes on.
One thing I always do when UV mapping is I plain map first, then select by group and shift everything off the map space. Then I map each part seperately, using plain and cylinder mapping mostly. The tricky part with guns is getting the flat areas at the top and bottom, and the ends of detail - basically all the stuff that a plain map doesn't pick up.
If you plain map from the side, you can then seperate the flat parts by selecting and deselecting polygons. For example the magazine on your M4, if you plain map that, then select only the middle polygons it would leave the sides, as a thin line all around. Then if you plain map from the front with just the leftover line, you get the other detail. Splitting off each side, then stretching out the bottom part would let you add much more detail. The thing is that in FPS view, the hardest parts to UV map are the most noticable, so crack UV mapping and your guns will look much better.
It takes a lot of practice to get good at UV mapping, but anyone who needs it will suss it out, especially with Lithunwrap, as that's pretty awesome for a free package. I use the newer Unwrap3D, which has an integrated preview, you can select polygons and see them selected in the preview, it's a very very handy tool. Worth investing in, in fact it's about the best purchase like that in ages.
When it comes to the texture itself, I tend to save the UV map as a .PSD, then in PaintShopPro, I load it up and make the UV image a lighten, and draw the detail on layers below that. It's hard to avoid using a photograph, but really the best guns are drawn from scratch, using good metal textures and a lot of care. The main benefit in drawing your own textures is that your not stuck with the extra detail that you don't get with the profile photo's. I suggest grabbing JFletchers free gun model from the TGC store, and checking that out - it's an awesome model and even better texture map. I learned a lot from just loading up other peoples models and seeing how they UV mapped them, it's really the best way to learn I think - load them up and have a good look at how they did it, practice on your own models, and experiment with the different UV map tools. I tend to have the model loaded into Deep Exploration while I texture, I save the texture file and it gets updated in Deep Exploration automatically, so I can see the results right away. The demo version of DE would be fine, you don't need it to export, just to show a preview of your models.
I say again though, nobody that likes Lithunwrap would regret buying Unwrap3D, it's like Lithunwrap's smarter and better looking big brother. Learn Lithunwrap then consider getting that, it saves an incredible amount of time and stress.
