C 6.5 = caliber 6,5mm,
21733.10. = Protocol-No. 21733 Vienna proof house from 1910.
5633 = Serial-No.
The crown shows a "Frstenkrone" (crown of a first), therefore Prinz Leopold isn't possible. My opinion is "Frst von Lobkowicz" but not certain.
You can ask the proof house Vienna about the history regarding the protocol-no.
mailto:office-wien@beschussamt.gv.at?subject=Beschussamt Wien
https://www.bmwfw.gv.at/TechnikUndVermes...samt%20Wien.pdf

Last edited by Ger; 03/14/17 08:06 AM.