I just did a bit of research - it is the Remington Tactical that has a steel receiver, Mossberg 590A1 has aluminum, anodized receiver.
Jack Black and USMC Grunt are correct, I was wrong and I stand corrected.
No I don't own a 590, I've owned a 500 20" Persuader and currently own a 535 with a variety of barrels. My HD shotgun is a Remington 870 Marine Magnum. Sorry for the confusion.