skipper wrote:Nice group by any measurement, for sure. A .204 doesn't make a .204 hole in paper. It's more like .195 or so. Subtracting .204 from an outside to outside measurement will result in a group size smaller than it really is. Measure one of the holes on your target and subtract that from the outside to outside measurement. We've had this discussion before on this forum a long time ago.
What skipper has quoted is the only way to even come close to an accurate group measurement for Internet consumption. Even then, the use of a Sweaney-Type reticule ruler will help refine those measurements out beyond one decimal place and make them more accurate so they can be accurately described.
Guessing where the center of the holes are and marking them with a felt tipped pen, and the various other individual "techniques" that get tossed out as tips on how to measure groups, all give you an answer, but seldom is the answer even remotely close to correct.....sometimes not even to the first decimal place.
If you can visualize it, a 0.1XX inch group means that a round bullet hole of any diameter has been elongated and is out of round in some direction by 0.1XX inches. Accurately measuring outside to outside whether the group is one hole or whether its a group of separate holes and subtracting a true/correct one hole diameter is the only way to get a correct or close to correct answer.
In sanctioned shoots, and depending on the type of sanctioned shoot, the diameter of bullet holes for the various calibers of rifles fired is finely defined and is understood by all shooters before the match begins. As a result, all 20 caliber shooters for example, get the same diameter deducted on their targets. And since all shooters fire on targets all made of the same type of target paper that are all attached to equal backing materials, the holes are typically identical in size from one 20 caliber rifle to another.
-BCB
Hold 'em & Squeeze 'em