All of the pressure from firing shotgun rounds is primarily directed at the chamber, which is part of the barrel, and thus steel. Alloys can work well if made and used properly, so I agree with the previous poster's assessment.
One day, when I get done paying my student loans, I want an Ithaca 37, just to try emptying the magazine by working the slide and holding down the trigger. That's gotta be as much fun as "bump firing" your AK47 clone.