ok. im looking to get a mag extention for a benelli M1S90 "TACTICAL". it has the 18.5 barrel. which +shot extention will fit flush(or close to it) with the end of the barrel? every idiot i talk to says a +4, but if you take the spring out and stack shells in the tube, there seems to be room for only 2 more(leaving a inch plus for the compressed spring). it has the factory 4 shot with the one extra round bring it to 5 now. the +2 would bring it to 7 which most 18" barrels can hold maximum.
not to be erogant, but i have owned almost every modern tactical shotgun there is and i know how many rounds go with A>length barrels etc... but with everyone telling me on forums that the +4 is the one in this case that would work has me alittle confused.