These are the MGs I have personally operated:
1. M60E2. This was a tempermental girl. If I made sure to tighten the gas tube before firing every 100-200 rounds and kept her lubricated she would work like a charm, but only if I sang to her the night before. Think I am making this up? M60s have souls, and mine liked to hear me sing. Otherwise she would screw up.
2. M249. This was without a doubt my dream Mg. Light, easily maintained, high rate of firepower, accurate as all get out, and easily controlled. Never had a single problem with it except for blank fire, where all weapons malfunction. No singing required, M249s have no souls.
3. M240. Everything good about the M249 can be said of this gun except the 240 shoots through walls. My only complaint? You had to remove the barrel to alter the cyclic rate. Other than that, kick ass! Again, no soul.
4. M2HB. All M2s have souls. They are also like cranky old men with enlarged prostates and new onset Alzeheimer's. You have to treat them with respect and decent care, or they will give you a very hard time. The guy mentioned above who could only get 3-5 rounds at a time may not know how to properly set headspace and timing. When I left my unit there were maybe 4 guys there who knew how to do it properly. As long as you know and love the .50 and always do a 9-15 round burst like John Moses Browning and the manual call for you won't have a problem. Just make sure to do a barrel change every 200 rounds of rapid fire.