This looks to be an impressive and rare pistol, so as no one else has, I will post a comment, however antique firearms is not a subject I have studied. 
 
I believe "carabiniers" were basically cavalry that carried a short carbine, which would be easier to handle on horseback than a full length musket.  Would these double-barreled pistols be carried in a holster, perhaps in a pair on either side of the horse's neck ? 
 
Why would one barrel be grooved and the other smoothbore ?  perhaps for different charges... say ball in one and shot in the other ?? 
 
The pistol has been restored;  to me the steel barrel seems over-cleaned probably with acid ?  But maybe this is the norm with regards to antique firearms ? 
 
Anyway, hopefully someone who specializes in this area will make an informed post...
		 
		
		
		
		
		
		
		
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