I have straight wall 44 cal. round that is close to 44 Russian dimensions with a strange rim I can’t identify. The base of the case extends about .030" past the rim or to put it another way,the rim is located about .030" above the cartrige base. Case length is about .960" . Case diameter is .452. Exposed portion of bullet is .427". Rim is stamped with a “5” at 9 o’clock,an asterisk at 12 o’clock,a “99” at 3 o’clock and what might be an"S" at 6 o’clock. It is a rather blunt looking round nose bullet with two grooves exposed. Overall length is 1.448". I’m guessing this is a 44cal. military revolver round manuf. in May 1899.
I think that your round is a 10,6 mm Revolver cartridge for the German ordnance revolver, made by Koenigliche Munitionsfabrik Spandau in 1899
The strange shape of the rim/base is called “Mauser A base”
While on the subject, why is it called an A base? Because the profile looks like a flattened letter A or was it some Mauser factory identification designation? Was there a purpose to it vs. a typical flat base?
Dennis–If I remember correctly the term comes from a DWM catalog of about 1900. They assigned names to the various base types: Mauser-A (as shown above), Mauser-B (Standard Rimmed), Mauser-C (Rimless), etc. I’ll see if I can find the catalog with the list. With any luck someone else will put up the list and save me from digging it out.