2-piper
Recommend that you refer to "The Modern Shotgun,"Vol,1 by Major Sir G Burrard, pages 31-35. These pages review the need for shotgun barrels to converge at 40 Yards so as to hit at the same spot. Also seen are illustrations of correctly designed barrel spacers.
William Greener in his book, "The Gun" 1834,also discusses the need for shotgun barrels to Converge.


Roy Hebbes