Ask any Army armorer fixing the guns being used in severe conditions... They use both 870 and Mossberg shotguns. The repairs run far more than 2:1 Mossberg to 870 per gun. At least that is what they have told me directly.

With all the 870s I have messed with I have seen exactly no broken extractors. I have seen exactly one broken firing pin. I have seen several that locked up because someone had reassembled them without staking the shell stops. And that is about it...

With far fewer Mossbergs I have seen about as many problems...

Mark Begich, Joaquin Jackson, and Heller resistance... Three huge reasons to worry about the NRA.