Raimey, It is smooth bore and chambers an RST 2-1/2 inch 16 guage shell very well. I did the index card method of measuring the chamber and it comes back 2-9/16's every time. I know that's not very scientific, but it is all I can do for now. When I get back home on Friday I will take it apart and measure accurately with calipers.
The seller was married to a woman that has been on 22 Safaris and she supposedly shot birds in Africa with it in the 1970's.
It looks identical to the gun listed in the following post:
http://thefiringline.com/forums/showthread.php?t=334956They offer other suggestions as to the maker. Maybe I am off base with the whole Sauer thinking. Seller said it was a Sauer Stalking rifle in 16 bore and I didn't know enough to say different.