Thread: overboring
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Old December 31, 2004, 10:07 PM   #2
HunterTRW
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Join Date: December 3, 2004
Location: The Lower Forty of Hill Country
Posts: 177
According to Bob Brister in his book, Shotgunning, The Art and Science, "Pushing a heavy load of shot through a small hole is simply inefficient; it creates more recoil, deforms pellets, and elongates the shot string." He also states, "The less traumatic and jolting ride the shot charge is given through barrel and choke, the less damage to pellets and to the shooter's face!"

Thus, some degree of overboring does make sense in terms of reducing recoil, pellet deformation, and shot-string length. However, he notes that 10-gauge boring (0.775) is too large to get suitable sealing with 12-gauge plastic wads.

Mr. Brister recommends having a gunsmith enlarge the inside diameter of the 12-gauge barrel (typically 0.729) by approximately 0.010, and states that this can work wonders in reducing felt recoil and improving patterns. He also recommends having the forcing cone evaluated at the same time and, if necessary, reducing its angle (in essence lengthening it). This also helps to make the ride of the shot charge, "...less traumatic and jolting..."

After having one of his own guns with a tight barrel diameter and a steep forcing cone worked on by a Seattle gunsmith, Stan Baker, (who slightly overbored the barrel and reduced the forcing cone angle) the effect was a slight increase in velocity as measured by chronograph. The net result was a gun that was much more pleasant to shoot.

Good luck, and good shooting!

Last edited by HunterTRW; January 2, 2005 at 08:22 PM.
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