Oh, yeah the 590M is the mag-fed version of the 590. It comes like that, and a 10rd mag comes with it. They sell a 20rd mag too, but it looks goofy as hell.

Adaptive Tactical sells a 10rd drum conversion for the regular 590, which looks pretty damn cool. https://adaptivetactical.com/collections/sidewinder-venom-conversion-kits

Oh, yeah the 590M is the mag-fed version of the 590. It comes like that, and a 10rd mag comes with it. They sell a 20rd mag too, but it looks goofy as hell.

Adaptive Tactical sells a 10rd drum conversion for it too, which looks pretty damn cool. https://adaptivetactical.com/collections/sidewinder-venom-conversion-kits