I like the design but the rate of fire is still to much at what you have it at. If you based this off the M60 then you should keep it to around its rate of fire which was 500-600 rpm. Even with that rate of fire the M60 needed to be fired in burst or the barrel would warp from the heat. the M60 was also a 2 man weapon, 1 carried and fired the weapon while the other carried the ammo and replacement barrel.
On the other hand, if you based it off the M249 S.A.W. then the rate of fire would be 750-1000 rpm but would still need to be fired in bursts.
I guess I shouldn't think to much about it...but a cadence that varies from 1500 rounds (already pretty fast for a light machine gune) to 3000 rounds (deep in minigun territory) and that is effective at over 1.5 kilometers? HOW? Is this a precision rifle gatling? Oh yeah, if you have 200 rounds belt fed with a 1500 rounds cadence, prepare to reload every 6 seconds.