The rifle is inspired by the sig. The sig rifles use a different iron sight which was correctly represented in the artwork of the gun available during the marksmen community challenge. The ingame weapon however uses a different sight.
The gas tube valve above the muzzle is also missing on the 3D model in game.
http://arma3.com/assets/img/challenge/02_arma3_marksmen_NATO_DMR_8mUMYpjI.jpg {F25759}