well, i dont know much about uv mapping (tried once. failed horribly.) but from what i do know, you take the 3D faces and glue them side-by-side, sorta. amirite?

so to fix it, i think i'd mean having to unwrap the arm again (not the hand too, dont worry) and make it so the side edges of the uv map on the arm (where the seam is when its applied to the model) is on the far side of the foream (a.k.a. the part rarely seen in-game, as opposed to the inner-most part that's facing up when he holds a handgun, if that makes sense)

think of it like unwrapping a cylinder: say there's a side A that's always seen and a side B that's rarely seen on the cylinder (like with the arms in cs:s). when you unwrap it you get a rectangle. you'd need to unwrap it so that the faces on side A are in the middle of the rectangle and the faces on side B make up the side edges of the rectangle.

see what i'm saying? lol, sry if this is making no sense. i'm having a hard time describing it. lemme know if a picture would be easier, lol. it might sound complicated, but it's really just a matter of unwrapping it with the edges of the uvmap being on a different part of the cylinder (or arm, in this case)