I was at the local firing range the other day, talking with an old, one-eyed gentleman at the next bench. He was showing me his "half minute groups" fired at 100 yards (mighty respectable shooting for someone missing his "strong" eye).
This got me thinking: any rifle enthusiast knows that "one minute" (of angle) is very close to 1" at 100 yards -- 1.0472" to be fairly precise. So, what would the equivalent in metric be?
Well, 1 minute of angle is 29.0888 mm at 100 meters. Given the difficulty of accurately measuring the centers of groups of holes in paper (let alone, the "fish tales" issue), I think a good equivalent is that 1 minute of angle is 30 mm at 100 meters.
Not that it matters: most the formal ranges (as opposed to open range or gravel pits) I've ever shot at would be very hard pressed to provide 100 meter targets (about 8.5 meters longer than 100 yards). The mechanical devices that hold the targets cannot easily be moved, and you cannot have some people 8.5 meters behind others when shooting, for obvious safety reasons.
So, given than most ranges in the US will allow only targets at 91.44 meters, one minute of angle is 26.5988 millimeters. This does not round nicely, other than to 25 mm.
Of course, the firearms industry is almost as bad as the printing industry in its use of different, archaic and (frequently) approximate measurements. Metric is creeping in faster than in printing, largely due to the US military metricating and wanting compatibility with our NATO allies. But new civilian items frequently are still solidly colloquial (e.g., 357 sig, 40 S&W).
Jim Elwell, CAMS Electrical Engineer Industrial manufacturing manager Salt Lake City, Utah, USA www.qsicorp.com
