This might be somewhat of a controversial suggestion, seeming that it's a controversial firearm in hunting and weapons enthusiasts circles. I reckon the 8.6 Blackout could be quite a unique cartridge in game.
8.6BLK (8.6x43mm) is the bigger, cooler brother to .300BLK (7.62x35mm), which we already have in game as the Fors Elite. Although I reckon the Fors Elite was a bit of a wasted opportunity to have some sort of supressor in game, maybe we can make it right with the 8.6
8.6BLK is best know for it's subsonic performance. It's specifically designed to shoot heavier .388cal bullets with extreme RPM at subsonic speeds using a supressor to keep it quiet.
The 8.6BLK can fire subsonic or supersonic rounds if a little extra range is needed.
What I would love to see in game is 3 ammo types for this specialized rifle, 2 subsonic ammo types and 1 super sonic. The 210gr supers would be an ideal class 3-7 round with a range of 300m (and a slight but noticeable increase in how loud it is to animals because of the supersonic crack of the bullet)
A 288gr Fractureing Sub would be a good class 4-7/8, with super high RPM the bullet can easily penetrate and expand very well within its effective range of about 150m
Finally, a 350gr copper solid for the big stuff from class 6-9. The 8.6BLK has proven itself in Africa on video by taking down Lion, Buffalo and Hippo so I reckon a nice heavy round for the biggest game would be great within a limited range of 150m
Now, for sound, I reckon it'd be easiest if EW just made the gun with a supressor as is. What I'd hope is that the 8.6BLK in game is in the noise range of the Vanques 45 or the bows, like the cross bow, with the supersonic rounds being slightly louder for the animals.
Now the drawbacks to the gun, seeming that there's such an odd focus on balancing a single-player game, the 8.6BLK is expensive and has limited range if it is to work properly and be accurate.
Ok that's the end of the book I think