I also tried that gun some time ago, but I didn't really like it. It has this bug/feature which makes it eject 10 shells for each shot fired. Also, the model lacks select animations, and looks funny in 3rd person view.
Anyway, I'm making my own version for my realism mutator pack. It's generally working nicely, but I'm suffering a lot of the same problems. Also, it hasn't been tested for network games.
To make it powerful enough for my needs, I redesigned the firing modes. It automatically loads up four shots when you're not firing. Then you can fire all at once (alt), in rapid succession (normal) or just have them ready. The problem is that you can't fire when a round is loading, and there is no way of telling it not to reload. So if you have four shots loaded, fire two, and pause a short time to aim at another enemy, it automatically reloads, so you won't be able to fire until you have three rounds loaded, even if two could have killed the foe.