Either that, or maybe they overheated and he had to switch guns. There is at least one vid on YouTube where a guy had modded a semi-automatic, rips off 100 rounds, stops, and says “time for a new barrel”, or something to that effect.
My guess is that he knew overheating was an issue. That’s why there were a lot of guns. I don’t know how many were fired.
The sounds on the videos seemed like 30-40 rounds at a time to me, but I have limited exposure to that type of firing.