Author Topic: How the heck.... (Read 1403 times)

Seek · « **on:** April 21, 2003, 05:12:09 AM »

....do you measure MOA?

I've always used, what I've come to know as, the "maximum spread" method. Unforgiving of flyers but simple. I've read about the "average radius" method, considered more forgiving when it came to flyers but, too much for my feeble brain.

The group shown below is an all to common example of my groups of late. I've been fuster-ated with the "boogers" (flyers) blowing out an otherwise nice group so I decided to give the "average radius" method a try (to maybe "cheat" my group sizes in an accepted manner) and the difference was so great I don't think I did it correctly. Then again, after reading claims of unimaginably tiny (by my standards) groups I wonder if it might be, at least, close.

I just did some reading-up on MOA calculations and my brain is smokin'. I'm more confused now than before.

Any help would be greatly appreciated.

I used a point about a quarter of an inch below the intersection of the grid in the center of the diamond for my center (if that makes any sense).

Just out of curiosity, how do most folks measure group size?

Thanks.
(Edited to highlight the shot in the black)

Jose Grande · « **Reply #1 on:** April 21, 2003, 08:48:59 AM »

Let's start with M.O.A.It stands for minute of angle. What it is is 1in. per 100 yd.
In other words 1in. at 100
2in. at 200
3in.at 300
& so on. A sub-minute of angle rifle is something a lot of folks want,wheather they can take advantage of it is another question entirely.
It takes training & practice to use such a rifle to it's fullest potential.

Measure your groups from center of hole to center of hole.That gives group size. Flyers can be caused by ammo,wind gusts,or any of a large number of other things.
The group you shot is good.That hole in the dark part might be called a flyer,but it is still a fine group.
Lone Yankee could put 5 shots in a group you could cover with a playing card at 500 yd. Or 10 shots covered with a dime at 100 in the X.These with a .308 Win. Mod70 HB Target Rifle with peep sites.
So a MOA is what it is. You shoot & measure & make comparisons using the info above.
Any more qt. just post & I will get back to yah!! Good shooting!!!

Seek · « **Reply #2 on:** April 21, 2003, 09:47:15 AM »

Well...

I downloaded the RSI Shooting Lab demo and plugged in the above group. It was a guesstimate but at a maximum spread of .90 it gave an average group radius of .27 moa.

I probably need to explain the reason for this topic. When comparing group sizes using the maximum spread method it became obvious the maximum spread method didn't reflect the true differences in group sizes. All .897 groups are not the same. There had to be a more accurate method. It dawned on me that must be the reason for the average radius method.

With such a difference in the results achieved through the two different methods I now wonder who's using what.

I guess my question is: When people refer to an moa group size are we talking about maximum spread or average group radius. There seems to be a big difference.

I appreciate it.

Jose Grande · « **Reply #3 on:** April 21, 2003, 01:02:25 PM »

I use maximum spread if I measure the group.

Bob_K · « **Reply #4 on:** April 22, 2003, 03:35:52 PM »

Don't confuse MOA, a meaure of angular displacement, with group size.

The easy way to measure group size is to measure the farthest outside distance then subtract one caliber to yeld the center-to-center measurement.

Jose Grande · « **Reply #5 on:** April 22, 2003, 07:35:22 PM »

That's right Bob. That gives center to center. I was thinking that but did't remember to put it in. :oops:

Seek · « **Reply #6 on:** April 23, 2003, 12:17:44 AM »

Bob, Thanks.

If I understand you correctly then the above group would be .897 minus .224 for the group size?

Is that the preferred method of group size measurement. If so then what in the world is all the MOA stuff about?

Seek · « **Reply #7 on:** April 23, 2003, 03:07:39 AM »

First off...

GB
If you'll send me the IP addresses of the above member I'll run a trace route and relay all pertinate info to you. The information will include a detailed map of the location of the computer as well as the ISP. You can notify the ISP and I'm quite certain they'll be most happy to help handle the problem.

Back to the topic at hand...

Bob
At a glance that sounded like a good idea (made sense to me). After giving it a try I was right back where I started. lol

I feel like I'm not doing a very good job of explaining the problem. Expressing myself through a keyboard is a major pain in the butt for me.
I'll try it one more time (just once more I promise). :grin:

We'll call the above photo group #1 for reference purposes and this next one group #2. (#2 is an old group, I don't usually save the actual targets so this was the only thing I could find that might help.)

What I'm doing is load developement and trying to record results.

Group #1, using the maximum spread method gave me the .897 group size. Group #2 was .898. Recognizing the measurements are approximate, just looking at my recorded data would indicate very similar results with the two loads (one factory, one a handload). However, I feel the load used for group #1 was much better than the load in group #2. The flyer in group #1 being the problem.

I realized my measurement method was misleading. For that reason I decided to give the average radius method a go (with some trepidation). With results like MOA=.270 and the like it made it sound like quarter inch groups, which they aren't (in my opinion).

So...I'm at a loss for an accurate way to document my testing results.

Jose Grande · « **Reply #8 on:** April 23, 2003, 06:03:56 AM »

M.O.A. is 1in. at 100 or 5in. at 500 as we went over before.A group that is .897 or .898 at 100yd. is less than a m.o.a.
MOA or less is what everybody wants in their target rifle.
So you're doing just fine.

Bob_K · « **Reply #9 on:** April 23, 2003, 03:28:56 PM »

MOA is an arc measurement, and the best place it comes into play is in sight adjustment. Say your group is 3" high at 300 yards. Your sights say 1/4 Minute. What they mean is that each click is 1/4 " at 100 yards, 1/2" at 200 yards, 3/4" at 300 yards, etc. Four clicks on your sight will center your 300 yard group. That 1/4 Minute on your sight is 1/4 MOA.

Group measurement is usually center to center. Take the extreme spread and there is a 1/2 bullet diameter at each end, so that is why you subtract one caliber. It is important to state the distance the group was fired at. A .878" group at 50 yards is ok for .22LR, but starts getting really exciting at 200 yards, regardless of caliber.

You could express your group as an arc measurement but that clouds the issue. Just because you shot a one minute group at 100 yards does not mean you can expect to shoot a 5" group at 500 yards (another one MOA group). You can hope it, but the ammo loses velocity, is subject to wind drift, loses stability, etc, etc. Interestingly, there are some loads I've seen that are less accurate at 50 yards than the very same load at 100 yards. Obviously the load needed some distance to stabilize and fly right!

There there is the issue of statistical validity. Did you fire enough rounds in the group, and enough groups, so that you can say with certainity the group you are so proud of is truely representative of the groups the ammo/gun is routinely capable of, or was it just a fluke?

Just some things to consider...

Jose Grande · « **Reply #10 on:** April 23, 2003, 07:48:02 PM »

Bob, your last was a wonderful post. You are welcome here anytime!! :grin: I hope we can get our fellow shooter all lined out pretty soon,before he wears out a keyboard asking questions. :-D