This unusual rifle camera is a vintage Leica Gun with 400mm Telyt lens. Apparently, these are quite rare. Seems to be just the thing for a photo safari. The Leica Gun will be up for auction next month as part of the Tamarkin Photographica Rare Camera Auction.
UPDATE: BB reader Stephen Kupiec writes, "While Leica rifle cameras are rather rare, KMZ Russia produces the PhotoSniper series of Zenit SLRs with Tair 300mm Telephoto lenses mounted on rifle stocks."