Sandstorm's SKS has always bugged me. As far as how it functions in the game, it's fine. As far as the SKS's use in modern conflict, there's a large inconsistency. Sandstorm's SKS pattern is not used in the Middle East. There are a few clear clues as to which SKS it is, the most obvious being the detachable magazine.

The only variants with a detachable magazine are Chinese off-brand SKS rifles that aren't technically an SKS. Plus, the variant closest to that which is in the game is the Type 84/SKK.

The second most obvious is the barrel length. The normal SKS has a twenty inch barrel, while the game's SKS's barrel is on par with the AKM (sixteen inches). Granted, some AKMs' barrels are roughly fourteen inches, but I think that is where the slight difference in muzzle velocity comes from.

I will give credit where it's due, though: the devs did a really good job with matching their SKS to the Type 84 SKK. This would be fine if that weapon pattern was actually in use in the Middle East. Unfortunately, it's not in use there. It's not in use anywhere. As this thread details, the Type 84 is extremely rare, and the scarcity of the mags exacerbates their impracticality.

I just want a nice ten round internal magazined SKS with a twenty inch barrel and therefore a clear difference in muzzle velocity. I don't want this rare Chinese paratrooper crap.

The SKS in game is indeed a Chinese one, one need only look at the bayonet to verify that. The gun in game seems to be the Norinco commercial version, as can be seen from the spike bayonet and the woodwork.

IIRC, the Chinese versions of the SKS are more common since they were the only ones who actually used the gun for any length of time. The Russians just immediately replaced it with the AK and never really bothered to use the gun in any appreciable capacity. The design was transferred to any number of groups and countries, but was dead on arrival in the Soviet Union.

It being Chinese also makes sense in that Norinco guns and ammo are one of the biggest sources of arms and ammo for middle eastern groups, so you'd be more likely to find the Norinco export than the rarer Russian versions, since the Chinese used (and still use) it the most and continue to manufacture the rifle.