I believe, from viewing the schematics on the O F Mossberg website, that the guts in the 500 series are identical. The differences being in that the 535 and 590 are outfitted in camo and with black synthetic stocks respectively.
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George...
I am pretty sure that the magazine on a 590 is built differently, and by differently I mean heavier. If you are looking for a gun to hunt or shoot clays with, a 500 will do the trick. I have 3 and I love them. I suppose if you are looking for a purpose built defense gun, the 590 specail purpose (I think they call it) would be something to look at. For my home defense gun, however, I use a 500 with an 8 shot magazine and 20" barrel with the Hogue pistol grip and forend grip. It all depends on what kind of money you want to spend.
i have a 590, holds 9 rounds, shoots clays well, shoots buck and slugs well. light shotgun with never a hitch or any problems. my favorite shotgun out of 5.if i had a choice between 500 and 590 i would take the 590
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