Rate of fire for guns in general decreases with fps. This is real obvious when shooting with the GAU-12 sitting on the landing strip. Shooting out over the sea keeping the aim above the horizon the 1000 round magazine empties in 20 seconds. Turning around and aiming close to the ground close by it took 50 seconds. It is also easy to hear the rate of fire decrease in the same scenario.

With a lower end computer I also experienced this with the Zafir 7.62. {F22430}