In the last two issues I’ve detailed how to slug handgun barrels so lead alloy bullets of the proper size will be used in them. However, that’s just one of the factors involved in handgun accuracy — especially revolver accuracy.
Revolver cylinders add about another five to eight dimensions to the mix, depending on how many chambers are there and how uniform they are. Long ago I learned just matching a lead alloy bullet to a revolver barrel’s groove diameter did not insure it would be delivered to the target with precision. For instance, I slugged the barrel of a 1960s vintage Colt SAA .45 right at its nominal .451″. Therefore, I loaded my .45 cast bullets to .451″ and got disappointing groups.
For many years, I just blamed it on the .45 Colt as being a cartridge of inherently poor accuracy. That was nonsense. Finally I figured out the problem was Colt .45s of that vintage (and today) have notoriously large chamber mouths. I just took a break from this keyboard and measured all six chamber mouths of my 1967 vintage Colt SAA .45. — they were all .456″.
If you start a relatively hard .451″ bullet out in a .456″ chamber mouth it’s going to get slammed into the barrel’s forcing cone cocked off its axis. My solution has been twofold. If .45 Colt bullets must be hard (Brinell hardness number 12 or above) then I size them .454″. Conversely, if they can be soft, say of 1-20 tin to lead alloy (BHN of 10) and used at speeds under 1,000 fps, then they can be sized .452″. The pressure of powder ignition will cause softer bullets to obturate or fill the chamber mouths.
By Mike “Duke” Venurino
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