I dont think its a UV mapping problem at all since having no textures at all still produces the same thing.
here is what I think:
1) Its some sort of export problem (even though the .x still works as an object entity)
2) Model has issues/ too many layers/too many polys/not optimized or some sort of illegal geometry. (this is almost impossible since everything is crease optimized and such, and once again object appears fine in FPSC when not a weapon)
3) there is some unkown issue with weapon creator for whatever unknown reason. For a mysterious reason my user created meshes are showing up and being imported as amorphous objects when using weapon creator
4) the secret cult of FPSC nazi devs dont want me to use my own guns and want me to spend tons of money on model packs. Codemaster is in on it too
(jk...sorta)