I just bought a new Benelli M1014 , assembled it as per manual, lubricated it fully, engaged the safety. cocked the weapon, inverted it to load.......BUT, it takes only four 2 3/4" shells with the 5th going in the tube but won't lock. what am I doing wrong? the last shell is inserted in the barrel as instructed, hence 4+1. thanks for your help WRS