There was an alternative rule with a chart that was printed in either Demonground Magazine or Challenge that used a single roll for autofire with the result of the roll determining the number of rounds that struck. That seemed to work good for our gaming purposes. But there are lots of things out there. If you want to go off the deep end you can try Gunmaster or Phoenix Command; very cumbersome and over the top for simple roleplaying. But Gunmaster is hailed by a handful as the end all be all, Gods gift to roleplaying and combat simulation, not my groups opinion. But I can't post my groups opinion about it.

The autofire chart was the middle ground and I have heard of other methods but they all just over complicate it, some so much so you might as well use Gunmaster. The thirty or so players I have had around all like the autofire chart over anything else. I'll see if I can find it for you if you are interested. Been way to long since I have played Twilight 2000.