Calculating MOA

John, the original inch per hundred yards for MOA numbers was established a century ago by the NRA target scoring rings spaced in inches a target ranges in hundred yard increments.
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The fact that the NRA measured scoring ring increments in inches (the standard distance measurement in the U.S. for that scale of measurement) in no way implies that 1 MOA is an inch at 100 yards. It just means that the NRA chose to use inches (which was really the only logical choice) for laying out their target dimensions.
Remember your internally adjusted scope doesn't move the line of sight per click exactly as claimed. Neither does any other. The same make and models don't all adjust the same, either.
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I agree. Which is why all this: "That was cause for sight makers to make them move in amounts ... the mount spacing." doesn't really mean much. The nominal sight adjustment amounts are all just that--nominal.

It's certainly convenient that 1MOA and 1" are fairly similar in magnitude at 100 yards, but it doesn't mean that they're equivalent.

What's even more amusing than thinking of benchresters--whose hallmark is extreme precision in every respect--being happy with an approximation that's in error by about 5% is to think that if the U.S. had adopted the metric system in the early 1800s, this discussion would be about the validity of approximating 1 MOA at 100 meters as 3 centimeters. (Which, by the way is actually a better approximation--it's only in error by about 3.1%.)
 
Both benchrest shooting organizations (IBS and NBRSA) consider one minute of angle to be exactly 1 inch at 100 yards and even multiples for each 100 yards further.
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Wow, that is pretty stupid. Sure enough, you have to pick it apart a bit in the rules, but 1" = 1 MOA at 100 yards. http://nbrsa.org/sites/default/files/RuleBook_ByLawsV38_0.pdf

I don't know why they even bother mentioning the two different increments and for the life of me cannot determine why they have opted to intentionally confound the two as equal when they actually are not.
 
The "precision" in benchrest is measuring group sizes to small fractional units. Not what the unit of measurement is.
 
Wow! There is a lot of brain juice flowing in here! Thank you for the responses and for the great read. I am not terribly into precision, I just know the sound it makes when it kills a deer. Hopefully someone will get that reference... At any rate, I only wanted a ballpark of where the rifle was at and I am fairly certain that I am there. Many thanks to all who were able to help. I hope you all have a great Thanksgiving!!
 
My question has probably been answered earlier in the thread, but, here goes.

Is there term for the group's average distance from the point of aim?
 
Yes, or almost.

The most common way is to calculate the average shot hole distance from group center. The term is "mean radius" and that's the average distance bullets will miss the point of aim. It assumes the rifle has a good zero on the sights. A number twice that of the mean radius is a statistical value for an average group size.

Arsenals use this method shooting a couple hundred shots in one group, find the group center then measure each shot hole's distance from it. The extreme spread of the two widest shot holes is typically 4 to 5 times that of the mean radius.

Ammo is shot from barreled actions laying in a V block which eliminates all human interference as well as the variables rifles introduce. The objective is to test only the ammo. Barrels used are precision made. The 30 caliber match ammo so tested at 600 yards would shoot virtually the same accuracy level in well made rifles clamped in mechanical rests.
 
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Is there term for the group's average distance from the point of aim?
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Yes, it is called "I Missed":D

Sorry, this is actually a good question but I just could not stop myself. If you measured the distance of each shot, added the total of that, then divided by the number of shots you could break it down to MOA or MRAD.
 
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