Sauer is a German make of top quality for the discriminating gentleman, sometimes having interghangeable shotgun barrels as well as telescopic QD mounts. All I believe for the inter-war German shooter restricted as he was due to laws etc, the big boomer was for deer/boar and the optional shotgun sXs barrels for fowl.
Someone in our Club paid AUD$5000 for a more inferior specimen than yours 5 years ago, the ammo came from Switzerland in sealed dinky packets.
I shot a few rounds, the blast and recoil was high though. [Not for me I think.]
Definitely a collector's item.
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***Big Bunny***