Hello, I'm new to the forum but I've had my benelli M1 since 1997.
I might have an answer to the problems your friends have about jamming. Dirt or fouling isn't the cause.
About 6 years after I bought mine, it wouldn't cycle even when using big loads. We traced the problem to a small O-ring attached to a small pin at the back of the bolt that keeps the firing pin in place. If you replace that o-ring you shouldn't have any problems at all. You should be able to find that 0-ring at any car shop.