Midway USA has a lot of neat gunsmithing videos. Check out their site for the full videos. They often “chop them up” into smaller pieces on Youtube. Many, myself included, find the tiny videos annoying.
Well, they went ahead and put their AR build videos into two larger videos – upper and lower receiver. Now, they still have the intro graphics for each mini-video, which could have sped this up a bit, but it is good, solid information.