Hi 
The brass casing looks very like an old shotgun cartridge, these normally have some information on the base, is there anything there 
You could measure diameter and get gauge of cartridge and then purchase a similar cartridge to get the older brass look 
These cases were from around 1880 till the 1920's, I think 
Nice knife 
Regards 
Ken
		 
		
		
		
		
		
		
		
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