it already is better then COD they use a 5 year old engine(modified). Btw if you are doing skin textures mind the different tonesand use 512x512 as minimal standart.or atleast 256x256.
(are the arms in a different Texture map or the same as the gun?)
I'm assuming they are their own UVW. That way, they can reuse them for every gun. Otherwise, they'd have to re-unfold every UVW and do it by hand. Not only does that make it look inconsistent, it also adds a lot of unnecessary work.