[L473ncy]

From what I understand it's exactly like what it sounds like.

Due to the gas in the mag expanding it "cools down" (simple high school physics, compressed gas gets heated up, and when it expands it cools down) and results in a lower FPS. Only way to stop it is to keep the mag at a constant temperature (or at least try to) and shoot in single shot.

If you notice when using those mini green Coleman propane tanks if you go camping they feel cold after you've been using it for a while to cook food (sometimes it gets so cold as to form "ice"). Reason is the liquid propane is expanding into gas and getting fed into your propane stove so that you can light it on fire and cook your food.

I don't think that video demonstrates cool down at all. Now if you were to chrono before and after and there was little difference then I could see that there is no/little cood down but that video just shows a stress test.