minute of angle question

[Michael R.]

hello,
i have a question that i have been wondering about for a while. when i see pictures of some of the groups people are getting, .0042 with a 30-06, .0016 with a 204 and things like that, i think: how can people get these groups when the diameter is a 30-06 bullet is .308 inches and the diameter of a 204 bullet is 204 inches.if you could help me answer this question that would be great.
thanks

 

[Michael R.]

actually, i meant .16 inches with the 204

 

[jmr40]

You measure from the centers of the 2 holes the greatest distance apart. Or, you can measure from the outside of the holes, then subtract the bullet diameter to get the measurement.

 

[Sako Shooter]

You will find various opinions on how to measure groups. There is software that actually does it now. However, what I do is measure the diameter of a bullet hole I have shot at the target, which is usually slightly smaller than the bullet's actual caliber. For example, a .22 caliber bullet may make a
.209 hole or what not when measured with calipers.

Then, measure the group from the further outside diameters and subtract the bullet caliber that was originally measured.

I have actually shot from 25 yards a group that was as close to a "zero" as you can get. I did it once and it was really all bullets in the same hole. The reason for subtracting the caliber is that if you didn't, then even if all bullets went into the same hole, you would never have a chance to shoot better than .209 group (or whatever caliber).

Some just measure center to center in any event.

I recall when I first starting shooting groups, I used a ruler and didn't realize you had to subtract the bullet caliber or measure from center to center. I was actually measuring all groups from edge to edge, with no subtraction, and was frustrated I could not shoot 1/2" groups or less no matter how hard I tried.

 

[JohnKSa]

Then, measure the group from the further outside diameters and subtract the bullet caliber that was originally measured.

Rather than using the nominal bullet caliber, I recommend that you actually measure the diameter of the holes in the paper if you use this technique.

For one thing, the nominal bullet caliber may not be the actual bullet diameter. Secondly, I've noticed that bullet holes in paper aren't always the same diameter as the bullet that passed through them. In my experience the holes are often significantly smaller which would result in an underestimate of group size.

 

[chrome_austex]

Those tiny groups are measured center-to-center.

center-to-center allows easier comparison of groups at different ranges as well.

 

[quietman]

I recall when I first starting shooting groups, I used a ruler and didn't realize you had to subtract the bullet caliber or measure from center to center. I was actually measuring all groups from edge to edge, with no subtraction, and was frustrated I could not shoot 1/2" groups or less no matter how hard I tried.

Hee hee. You aren't the only one that made that same mistake early on.:banghead:

 

[Tirod]

There are different standards in determining group sizes. The Army requires ten shot groups and measures deviation in an entirely different manner.

The internet seems to prefer the best possible three shot group measured in the smallest possible way - whether it conforms to standard principals of statistical analysis, or not. Some even go out of their way to justify some arcane work arounds.

If you're shooting for gold, you live with the method the official scorer uses.

 

[jmr40]

Unless you are shooting groups where there is only 1 ragged hole in the target the easiest method is to just find the 2 holes the greatest distance apart and measure from the inside of one to the outside of the other. This automatically takes into account bullet diameter and will give you the group size center to center without doing any math, or guessing where the centers of the holes are.

That is close enough for me and the type of casual target shooting I do.