With regard to the rifle, nominal caliber can only be precisely identified with a chamber cast ( and "slugging" the barrel) as suggested by Raimey. There was a 9.3x82R mm, but not as common as the 9.3x72R, both of which were mostly found in German rifles. The 9.3x57R ( 360 2 1/4 " British) was a common caliber in Belgian guns also. To complicate matters more, 9.3mm might be the bore(not groove or bullet) diameter for a nominal .375" or 9.5mm caliber. I agree with skeettx that the gun can likely be made to function w/o great expense. Low pressure 16 ga 2 1/2 shells are available ; or a "Little Skeeter" type chamber insert in 20-28 ga or .410 bore can be used if you are afraid of the barrel. A "hands on" examination is required.
Mike