The DC-17m Sniper, is an upgraded version of the DC-17m with a sniper attachment (hence the name).
They were used by the Republic Commandos during the Clone Wars, and each rifle could have five rounds per magazine. It functioned at two levels of zoom: 10x and 20x. The sights also provided an x-ray vision effect to locate vital targets within the enemy.It was a useful weapon to have around on missions requiring stealth, such as assassinations or thinning out enemies.
The DC-17m sniper attachment was also the favored weapon of RC-1207 (Sev) of Delta Squad and RC-8015 (Fi) of Theta Squad (also known as Omega Squad in non-canon references.) Both which created the attachments.