Ok, here are the fotos of the buttplate and others.  
All brass items are fixed with small brass nails. The foto with a very similar spring at the inner side of the lock I found in the book of Keith Neal, Spanish Guns and Pistols, Foto n°52.  
 
Thanks für help. 
corrado26
		 
		
		
		
			
		
		
		
		
		
		
		
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