Mine was doing the same thing, right about when the rim hit it would get really tight and then you could push past it. A little searching I found this out of the UK. I did it and now its buttery smooth loading shells. It also shows how to change out the carrier.
go to : forums.pigeonwatch.co.uk/forums/index.php?/topic/87374-benelli-m2-tweaks/
I cant link yet sorry..