The video is about 20 minutes, and goes over the details of semi and full auto fire. The semi-auto operation is the same as an AR-15, so if your wondering how one works, here’s your answer.
Incidentally, it looks like the army needs to work on gun safety, especially in regards to KEEPING THE FINGER OFF THE TRIGGER. Oh well.
Legal boilerplate: With a few very specific exceptions, converting an AR-15 to full auto is ILLEGAL. If you use this information to try it, don’t blame me when you get in trouble.