Phewww, I had one that I wish I had never sold...they're not gas-operated, at least the one that I had wasn't. It was a great gun, and I was a jackass for selling it.
I replaced it with a mossberg 9200 - not worth it.
I currently have an SKB o/u that I like a great deal, but if I'd had the sense that god gave a mule I'd have the semi and the o/u today.
Cheers
Mac