First off, the picture in that link, shows a light barreled gun. It is not as heavy a barrel as mine is by any stroke.

SRY can't help with the 590, however I have an model 835 (combo) and it has very heavy barrel walls at the breech and a 24" fully rifled tube - very accurate, even with 3" 1 ounce fosters at 1,780fps. Due to the heavy breech it is said to be suitable for some of Ed Hubel's AA Steel Powder loads of 600gr. at up 1,900fps, depending on case length. It is chambered for the 3 1/2" hulls.
The extra barrel is a vent rib 28" with replaceable chokes.
Mine is walnut, not plastic nor camo - older model.