Kind of strange. I have two identical shotguns (M500A Flex Security). Both have about the same round count on them (less than 500 rounds). One of them will hold 6 shells in the magazine tube, the other only 5. They have both been like this since new. The Magazines measure exactly the same length. The shells are all the same length (just different brands). When I compare the magazine springs...they both appear to be the same diameter and coil count, though the spring on the shotgun that only accepts 5 rounds is actually about 3/4" shorter. I swapped the spring from shotgun (B) that holds 6 rounds into shotgun (A) that only holds 5 rounds and it made no difference. Question: What might be the reason for this disparity? Both shotguns have the same follower (Factory swapped out for NDZ).