So the Benelli M4 is a little different when it comes to manual cycling.
Without pressing the trigger, the next round will NOT manually cycle into the barrel.
In this way it's much different than typical pump shotguns, or most any other gun on the market.
This is designed so that in a LEO situation, after firing a round, the officer can eject the live round from the chamber and keep the remaining rounds IN the mag without loading the next round. He can then put the gun back on safe without a live round in the chamber.
This guy outlines it best, copied shamelessly from the Benelli USA forums:
"Your M4 sounds fine...You just need to get used to how it operates....the cartrige drop lever allows you to change to say a rifled slug by port-loading it instead of it feeding the next round in the mag tube. (by not pulling trigger on the chambered round and not pressing the cartridge drop lever you can eject the round in the chamber without the next one in the mag tube feeding)
The rounds don't leave the mag tube and go onto the shell lifter unless the trigger is pulled. (or cartridge drop lever depressed)
Bolt should lock back when empty if the last round was fired. if it was ejected without being fired (like when changing out a round) it doesn't lock back
The shell lifter is only not allowing a round to be fed into the mag tube if you have dropped the hammer say on a dummy round and the bolt has not cycled. As soon as you rack it again (simulating a fired round you'll see that it will allow you to top off the tube.
A lot of people new to Benelli have this issue so no worries. Play a little more with dummy rounds and remember to pull trigger if you are trying to simulate a round firing and it will all become more clear."
https://forums.benelliusa.com/topic/...t-im-not-sure/
Hope this helps,
Josh