Hrm...I was thinking it looked more like SS. I thought the hardchrome ones were raw brass inside, but I guess I'm wrong. FWIW, I have a 12" SS J&J for my Pro-Lite with spiral porting, a slightly different type of muzzle brake, and no internal rifling. Heavy as hell, but it shoots beautifully with most of the small paint that's in fashion these days. I also had a 14" raw brass, internal straight rifling (4 lands, like yours), completely unported barrel on a Maverick way back when. That was an amazingly accurate barrel, even with lousy paint. Again, heavy as hell (esp. on such a light pump) and LOUD, but I rarely needed more than one shot to hit anything with it. Usually there would be a deafening crack from the end of the barrel, followed by a disgruntled-sounding "out" from across the field.
I really wish I'd never sold that gun. Or the barrel.