Hi Adrian 
 
Yes, your experiment makes things more clear.  I was under the impression that the hook(s) were moveable.  But as mentioned, they are not.  I can now visualize the bow lashed with leather throngs.  It would seem to use a fairly long arrow.  This would seem to be a period experimental piece.  In theory the bow/arrow arrangement used as a backup once the gun was fired and not enough time to reload the gun.  A different idea on the superimposed guns from the period. 
It's certainly an interesting piece.  And likely the only known surviving example. 
 
Ricck
		 
		
		
		
		
		
		
		
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