ya gotta think of unwrapping logically,think which parts are most important and which are no so,at the moment I think you have leaved to much space for the buttons where other things could use the space....and take it from there.
How are you planning to have the charcter carry the gun?
(will it just be in the corner of the screen (normal style FPS),or will you have an "iron sight" view?)
If its just gonna be in the corner where only part of the gun is visible on screen then you should dedicate a larger chunk of your texture space to those visible areas...if your gonna see the side of the gun while reloading then give more to texturespace to the side taht will be visible....think like that.
If ya not sure what I mean,think of it like this,if you model and texture a car for a racing game,in the game the car cannot roll over...how much texture space would you dedicate to the underside?..a plane small sqaure somewhere on texture or a space thats the same size as the very detailed top texture.
the above may also apply to the cocnept of your gun,in that if one side of it is never visible,why ya got the polygons there?....delete them and save on the specs.
Hope that helps