1up Spacing was usually 1/4 So every fifth round was a tracer. It still looked like a red line due to the amount of ammo going through.
As Nick will tell you nothing could make one more mad than a jam. Seems if you release the trigger prior to the limiter switch they seem to eat bullets in the mechanism.
I think today thats pretty much history.
By the way that video was put to gether near Maricopa Arizona by a company that is manufacturing mini guns. I dont know if its on their website but heres the address.
www.dillonprecision.com They specialize in great reloading equipment and are located on/near the Scottsdale AZ airport...
The owner has his own surplus UH-1 Huey and a MD-500D. Both in pristine condition last I saw.