The primer feed on the 366 is crappy, in my opinion. Sometimes it will drop more than one primer. However, it works pretty good if you wrap a rubber band around the end of the primer drop tube to keep some tension on it. Also, the powder will shut itself off occasionally. Of course, you will have a turret full of shells w/o powder before you notice.
The 366 for 410 bore has yet another problem. In addition to the problems mentioned above, the small base on the 410 shell allows it to wobble as the turret indexes, then the primer seater catches the edge of the shell as you pull down the handle and ruins the hull. It does the same to the shell that is being filled with shot. Of course, the shot then spills, and you have to remove the turret from the loader to clean up the mess. Its a good thing I was in my 20's when I had the 366. Now that I'm pushing 50, I probably would have a stroke if I had to deal with that beast again. Many times I wanted to take an axe to it.
I swapped a fellow straight up for a MEC 650. I was delighted to be rid of the 366, and I used the 650 for more than 20 years with no problems whatsoever before I sold it for $100 and bought a MEC 9000G.
I suppose, in all fairness, Hornady may have made improvements to the 366 since I had mine in 1985, but since the MEC's work so good, I'm sure not going to find out.