Powers Custom, out of either KC or Independence MO, built some of those for prairie dog shooters, back in the late '90s or thereabouts. There was at least one feature article about them in one gun magazine and I think the Varmint Hunter's Association magazine, too. It wasn't a new idea, it had been ripped off from the old water-cooled machineguns of WWI and WWII, they had to have a pressure manifold and pump system to pump the water from coolers thru the water jackets to keep the pressure the same for every shot, and they were complicated systems.
I thought it was kinda neat, but the price for a system, and the smithing for the water-jacketed barrel and assorted equipment was pretty pricey. I thought it was more practical to just buy a couple more rifles and swap them out when one got hot. I was doing a lot of PDoggin' back then, and read about it with a lot of interest, but no money in the bank for such things.
