Honestly just fuck this attachment.
So, for anyone who doesn't know, the Long Barrel makes most .308 weapons one-shot kill to the torso of a player at close range, even if he has Heavy Armor (the SCAR-H is the exception; it doesn't really do anything for that gun). That's my biggest problem with this attachment because it essentially adds AP ammo to the G3A3, M14 EBR, and FAL and bypasses armor entirely. For other weapons, the Long Barrel increases the hitscan range for weapons but that's not really necessary anyway. Rifles have an effective range of at least 120 meters and kills past that distance is the Marksman's job.
I think the Long Barrel attachment should automatically be equipped to the bolt-action rifles (as those are designed purely for damage at range). Remove the attachment for all other weapons just for game balance purposes. Maybe buff the M24 as well, as it's currently mediocre at best.