The thing is, because the price of the bullets, the M99 has become a moron magnet, because the noobs who use it WILL drain the teams' funds, and they will rage-quit if nobody supplies them with money, often with their knives out.
What needs to be done is to reduce the price of each bullet to 80 pounds, and cap the ammo max to 10 bullets. Increase the time between bullet reloads as well.
Another thing that can be done would be to reduce the price of each bullet like the previous suggestion, but instead of capping and increasing delays between shots, you can reduce the base damage to 210 and multiply the HS bonus by 3x.
Each of those ideas will serve to amplify the high-risk, high-reward idea behind the M99. The first one does this by reducing the number of opportunities you get to fire it, the second one by making body-shots far less viable and headshots that much more important.