Powder fouling + dirt + oil/water = sludge that will stop the gas system from working right. Gas operated shotguns need to be kept very clean to work reliably in extreme conditions.

What I found I like about my Stoeger 2000, with the Inertia action, is that as a function of how the action works the action actually locks up tighter immediately after firing. This seals the chamber very tightly and delays unlocking long enough to ensure that almost all the powder fouling goes out the muzzle, not back into the action. And since there is no gas system, the only part you have to worry about keeping clean is the receiver/bolt assembly. Gas guns have that AND the gas system to worry about. My Stoeger, to my pleasant surprise, actually stays cleaner than any pump gun I've ever owned because the initial ineria response forces the action to lock up so tightly.

My Stoeger is the best $400 I've ever spent on a shotgun. It's not as pretty as a Benelli, but it works just as good and cost 1/3 as much.

Mike