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Bart B. · March 13, 2014, 09:55 AM

curmudgeon1, calibration of the precision calipers benchresters use to measure their groups is easy. I've calibrated a couple of my own in a metrology lab on Jo blocks and noted any error. It's easy to measure groups that small as their outside edges are "blackened" quite accurately in the special tagboard paper used for targets; a single bullet hole diameter's blackened edge is exactly what the bullet is; within .0001". I've measured bullet holes made in that paper with bullets .3075" diameter (groove diameter of the barrel they came from) with a 20X loupe and their blackened edge is just that. Benchresters often use single bullet holes on sighter targets to "calibrate" their calipers for the group holes in the target.

Resolution is easy with magnifying glasses observing the edge of the caliper's caliber ring to less than .0001" As many precision machinists with high levels of skills and knowledge measuring tiny things play that game, they've no issues with scorers in stool shooting matches well qualified to meaure precicely to resolve dimensions to that level. And the average of several measurements ends up being close enough to exact and actual for benchresters' objectives.

March 13, 2014, 09:55 AM	#32
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	curmudgeon1, calibration of the precision calipers benchresters use to measure their groups is easy. I've calibrated a couple of my own in a metrology lab on Jo blocks and noted any error. It's easy to measure groups that small as their outside edges are "blackened" quite accurately in the special tagboard paper used for targets; a single bullet hole diameter's blackened edge is exactly what the bullet is; within .0001". I've measured bullet holes made in that paper with bullets .3075" diameter (groove diameter of the barrel they came from) with a 20X loupe and their blackened edge is just that. Benchresters often use single bullet holes on sighter targets to "calibrate" their calipers for the group holes in the target. Resolution is easy with magnifying glasses observing the edge of the caliper's caliber ring to less than .0001" As many precision machinists with high levels of skills and knowledge measuring tiny things play that game, they've no issues with scorers in stool shooting matches well qualified to meaure precicely to resolve dimensions to that level. And the average of several measurements ends up being close enough to exact and actual for benchresters' objectives. Last edited by Bart B.; March 13, 2014 at 10:12 AM.