Allow me to prove my ignorance. I am VERY new to shotguns but am looking for a home-defense gun. I notice that some SG's have a flap over the magazine loader port (including some cheaper guns) and some do not (including some more expensive ones). I would think this flap helps keep debris out, right? So why do some of the nicer guns (mossy) not have them, but cheaper ones (pardner, IAC) do? what am I missing?