pehaps you can link your new weapon to different decal files, these are images that im pretty sure are in the gamecore directory somwhere if you dont want to affect another weapon in fpsc change it after you have built your game in your games folder, that is of corse if you cnat just put a new decal in there and relate theat weapon to the different decal, if must be possible because the new segments have different decals to the old ones, althouth looking thta might not be so easy becuase i just noticed al lthe decals are in a bullet holes image, i believe if you took out a decal from this image you game does use and then replace it with your own then adjusted scorch type of somthing likke that in the gun spec it would set to correct, also you could edit the source code so a bigger decal file can be used, i would try it but i am yet to swimm al lthe way through the source code
Thanks
Adam