I have seen factory 12 ga. brass case ammo, presumably loaded with smokeless powder.  It was loaded for the military, WWII or later.  The only 'issue' I have heard about is that the i.d on some brass cases is larger than 'normal' and requires 11 ga. wads to get a proper fit. 
C.G.B.
		 
		
		
		
		
		
		
		
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