I'm not the most knowledgeable person to respond to this but I'll give it a try and make a suggestion.
The M4 has an interesting and sometimes confusing "manual of arms", at least to me, a non shotgun type person.
It is saying indirect because you are loading the magazine and then letting the shotgun action load the chamber. A direct load would be to pull the bolt back and drop a shell in through the ejection port, let the bolt go and the shell goes directly into the chamber.
You have to know about the cartridge drop because if the trigger has not been pulled and the shotgun has been cocked, you can rack the bolt all day long and it won't load a shell unless you hit that cartridge drop. This can be very handy for switching out slugs and buckshot.
So a suggestion would be to buy 4, or 5 or more Dummy shotgun shells and play around with them. Will help with your next task which is to learn Ghost Loading, it comes after the indirect loading lesson!
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