Impressive mag dump. It would be neat to see the M4 run a couple of practical shotgun drills at speed.
Set up 5 mini poppers at 15 yds 1 yd apart. If you can drop all 5 in 2.5 seconds or less you will be word class fast.
Another good test of practical shotgun skills is two poppers at 15 yds about 15 feet apart. Load two shells, one in mag and one in tube. Shoot one popper, load 8 shoot the other. 4-5 seconds is FAST.
Clays can be sustituted for steel.