Rokstedi, suppressor, VFG, drum mags, COAG, sling....
Off-topic: just for the record, I don't think the sling and the grip can be equipped at the same time, but I'll evaluate both anyways.
The Rokstedi is a semi-automatic assault rifle that is capable of more damage and range as opposed to its full-auto counterparts. Although it is slightly lackluster in close-quarters combat, it more than makes up for this inefficiency in medium- to long-range.
The COGA scope does a good job of augmenting these longer-range capabilities, while the vertical grip allows for lower recoil and improved steadiness. Drum magazines double the Rokstedi's current ammo count from fifteen rounds to thirty, which improves its use in extended combat. The suppressor lessens the noise generated by every shot. In conjunction, all of these components make the gun extremely hefty and hard to draw out, but the sling alleviates some of the latter.
As noted earlier, all of these parts make for one heavy gun. A Medium with such a weapon is not very reliable when on the frontlines because the Rokstedi is incapable of matching the fire rate of weapons like the Gerund or the Rhett; rather, he or she should be relegated to supporting a player attempting to complete the objective. Heavies with this build should only use this when a target is too far out of range for their machine guns or grenade launchers.
In terms of classes, the Operative is probably the class best suited for such a setup. After setting up traps, the Operative can then hide in a more secluded spot and pick off at enemy forces who have encountered said traps.
-----
A Barrett Light Rifle, outfitted with a four-vent muzzle break, a Snoop-R scope, and a sling.