MOA vs group size

[chaz12]

This is just something I'm curious about.

If you are told that a rifle will shoot with an accuracy of 1 MOA, I believe I've read that equates to 1 inch from point of aim at 100 yards.

Would that also translate to expecting group sizes of 2 inches? If the 1 inch deviation could be in any direction from the point of aim?

Chaz

[Bogie]

1" center to center, of the furthest holes = group size.

Or, conversely, for instance, if you're shooting a .30-06, measure the whole bit, and subtract 0.308.

Gun store commandos do things differently tho...

[Bitmap]

I believe that 1 MOA is approximately 1.047" at 100 yards. Twice that at 200 yards, etc.

1 minute of angle means literally 1 minute of angle, as in minutes and seconds of angles in geometry.

Groups are generally measured center to center of the two that are farthest apart, as noted. I find it easier to measure from the outside of one hole to the inside of the farthest hole.

Also, remember that just because a rifle once put 3 rounds into an inch at 100 yards does not make that a 1MOA rifle.

[Inspector3711]

Technically I believe that would be minutes and seconds of degrees. It is basically accepted that 1" is the approximation for 1 minute of angle (1/60th of a degree) at a distance of 100 yards. To be a 1 minute of angle group, the two holes farthest away must measure 1" or less center to center. When measuring between two holes it is required that you know the diameter of both holes. You measure from the inside of each hole to the other and then add a full diameter in this case because we know both holes are the same size. You can measure to the outside of both holes and subtract a diameter as well. Either method will give you the center to center dimension.

The location of the group in relation to the center of the target is irrelevant in terms of how repeatable the accuracy is and what size group it can shoot. Once a group size is determined, the rifle can be dialed in by adjusting the sights.

[22-rimfire]

I always measure outside to outside. I don't subtract for average bullet diameter. Guess my groups are better than I thought.

I have always wondered where the outside is precisely when you print your targets on regular paper. Holes aren't always like perfect circles like you get with wadcutters. The edge is always a little mangled. So is it the hole or the total circle of influence when measuring? Group measurement 101?

[Scorch]

I believe I've read that equates to 1 inch from point of aim at 100 yardsMeasuring group size is not a measure of dispersion from the mean, it is a measure of maximum range of variation. Point of aim is irrelevant in measuring group size. Point of impact (POI) could be 3 feet away from point of aim (POA) and still be sub-MOA as long as the rounds all impacted within 1.04" center to center. You see this in Benchrest matches, where POI and POA are typically about 6" apart.
Would that also translate to expecting group sizes of 2 inches? No. Maximum dispersion of 1 minute of angle, i.e. 1.04" at 100 yds, 2.09" at 200 yds, etc. You are measuring the size of the cone of dispersion, not the deviation from the axis for each individual shot.

[Bitmap]

Technically I believe that would be minutes and seconds of degrees.

Technically, a degree is 1/360th of a circle, a minute is 1/60th of a degree, and 1/21600 of a circle, so you can say "minutes and seconds of angles" or "minutes and seconds of degrees" of angles. Either way.

[jsmaye]

Maximum dispersion of 1 minute of angle, i.e. 1.04" at 100 yds, 2.09" at 200 yds, etc. You are measuring the size of the cone of dispersion, not the deviation from the axis for each individual shot.

Crud - all of my 1 MOA guns just became 2 MOA...:o

[62Aero]

There's plenty to love about a 2 MOA rifle