I've been using the silenced M4 with CCO for some time now, very happy with it. Ammo is readily available in military locations and thinning out the Z population with a silenced weapon while sneaking around is just great.
And for PvP IMO there's nothing better than a silenced, fully automatic weapon.
I've tried several sniper rifles (DMR, SVD) but they're far too situational to use for my tastes to justify carrying them around in the backpack.
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"...late afternoon the Air Tasking Order came in [and] we found the A-10 part and we said, "We are going where!? We are doing what!?"
Capt. Todd Sheehy, Hog pilot, on receiving orders during Operation Desert Storm