The 3 inch 20 was introduced after WWII.  I think in the early 50's 
 
So if the barrel are origin to the gun,  and are that light,  that is a lot of reaming 
 
Dean's question may be a critical one
		 
		
		
		
		
		
		
			
				__________________ 
				"If there is a heaven it must have thinning aspen gold, and flighting woodcock, and a bird dog"  GBE
			 
		
		
		
		
	 |