I was at a sporting clay course over the weekend and had one of these speciality rifles in my hands.  It's a double bolt double sxs rifle Blaser R93, when you pull the bolt handle straight back there are two bolts, which pick up a cartridge from each magazine and load it.  Two triggers fires them, extract straight back, picks up two more cartridges, ready for two more shots (Total of 8 rounds available).
It is quite heavy, but rather short.  Caliber I think was .416.  It definitely was cool.  How practical?  I don't know, but I can see the thought process.  Anyway, pretty cool, especially to have one in your hands, they don't give them away!!  Waidmannsheil, Dom.
More info at:  
BLASER 
R93 Duo Double Bolt Rifle
