I'll start with this - I was never able to get 5 rounds in to the thing before it had the +2, so the plus 2 is plus 2, but it is SOOO tantalizingly close - if there is something I have setup wrong or can fix i'd be interested to hear about it.
I compared every kind of round I have and found the shortest - "military 00 buck" sold in carboard 5 round packs at big 5, headstamp reads "winchester 12 GA" side says "9 PEL 00 Buck" in black on the OD green hull. seem like it might be actual made to mil spec 00 buck, which if true would be the exact right ammo for the gun right? it is taper crimped and almost exactly 6 CM in height (aka 2.36") - makes sense since the mil is on the metric system.
6 go in fine, #7 is ALmost there and is about 3-5mm from going in when it stops hard. I actually pulled the cap off to see what was going on inside the tube when I fed it, and I watched the follower approach the spring retainer, and the spring basically coiled togehter until the coils had no space between then and it literally couldnt compress any further and so between the follower and the cap the sprint was fully compressed and it was about 3-5mm short.
Am I missing something or does benelli have some shorter ammo they are spec'ing the gun with?