I don't know if mossberg changed this of if the 590 is different than the 500, but I've seen the pump arms break on the older 500 models. They are not as thick as the rems and twist more. Seen a couple break/bend. Mostly old military issued (thus grossly used) ones. The rems have that flat sprin on the inside of the receiver and the like to wiggle loose after equal abuse as the military mossbergs. FWIW, they're about the same. I prefer steel when I'm swinging it like a club though.