In the Rupp rifle I built last year, I used a heavy .45 cal barrel, and drilled the rod hole 3/8" It was a mistake...5/16" would have been better. It would have allowed me to slim the stock from the top of the barrel to the trigger guard. In the Kuntz. 40 cal I just finished, I had Dave Rase drill it 5/16" A much nicer profile. I had him drill the wood for my next Verner rifle, a .50 cal., 5/16" as well. Of course, he hit the web thickness right on at 5/32". The Verner is only 1.6" (by my calculations) top to bottom, so this will give me the profile that emulates the original. A rod tapered to 5/16" on the small end is lots of rod for a .50 cal.