Look honestly I've used the r99, and I've used it effectively. However it brings a call of duty time to kill into a game that has a relatively slow time to kill and it really just makes the game not fun when you come up against an SMG that can just take out a Gibraltar in purple armor befor a spitfire can fire 3 shots. And I know the arguments for keeping it the way it is would be that it's a close range gun, but if you have ANY level of recoil control it's a solid midrange weapon with the same absurd time to kill. Here are my suggestions for a rework:
10% rate of fire reduction
11 damage per bullet
Nerf the amount of ammo that that the gun can hold by 2 per magazine stage
Now I'm not a game designer so I wouldn't know if any of those would solve the problem, but I still believe something has to change, because even now I'm more scared when I see an r99 then when I go up against absolutely any other gun, which is saying something for its relatively common drop rate.