first

open with vtf edit the texture of the game with source engine, i will the ak47 from kuma war 2 mp

i use gimp for it use the layers and channels window like show the image use the tool for lighten or darken for do more white the texture 2 times until have a gray colour(if you uses this for a black weapon, if not skip this step)

the next step use the color`s flange like indicates the green arrow click on color balance put red in 9 green in 6 blue in 0

then use again lighten and darken for "burn" the texture until you have a brownish save as vft with the plugin then in the vmt file put the following keyvalues the texture that i used is called "ak471darkgold" and "ak471" is obviously its bump map:

(note: the important part in vmt file is the phong and envmap)

"VertexLitGeneric"

"$model"    "1"
"$surfaceprop" "weapon" 
"$basetexture" "models/weapons/whatever"
{


"$bumpmap" "models/weapons/weaponwhatever_normal"



"$envmap" "env_cubemap"
"$normalmapalphaenvmapmask" "1"
"$envmaptint" "[1 .8 .465]"

"$phong" "1"
"$phongtint" "[1 .8 .465]"
"$phongexponent" 7


"$phongboost"   "6" //overbrighten factor
"$detail" "materials/details/detailrust