Finally got out to the range. Shot Federal, Remington, and Winchester 00 1325 fps Buckshot with no feed or eject problems. Shot Fiocchi 00 Buckshot and had failure to feed and eject. It improved slightly. Rather than every third round having a problem, it occurred after every 5th round. Not going to buy anymore Fiocchi.
Benelli checked out my M4 and completely serviced it. They shot Federal, Remington, and Winchester 00 Buckshot with no problems. They said the gun had no mechanical problems.
I think you guys were correct. Fiocchi ammo was the problem.