That's the theoretically possible maximum rate of fire. Actual rate of fire appears to have been maybe 12 rpm with 30 round mags. Given 10 round mags, he empties a mag in 50 seconds, and takes 10 to reload. His rate of fire dropps from 12 rpm to 10rpm.
12rpm is way too slow. Thats a shot every 5 sec. Why should it take that long given largish targets at short range?
1 per second seems perfectly feasible given the circumstances.