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British Firearms (Pre. 1914) >> Breech Loading - Military Rifles >> Mean figure of merit.
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Message started by DoubleD on 11/17/05 at 2:16am

Title: Mean figure of merit.
Post by DoubleD on 11/17/05 at 2:16am

Looking at The Treatise of Ammunition 1887 under Martini ammo accuracy is defined as: The mean figure of merit.

Can any one point me to a reference defining mean figure of merit?

The figure given is 9".40

Title: Re: Mean figure of merit.
Post by dbm on 11/17/05 at 7:05am

I don't have a reference book to hand, but an article from a 1979 edition of Guns Review, when discussing the Enfield rifle has a definition.

The mean point of impact of a 20 shot group fired from a bench rest was determined by calculating the average distance of the shots from any datum point. The mean distance of the 20 shots from the mean point of impact was the figure of merit.

David

Title: Re: Mean figure of merit.
Post by DoubleD on 11/17/05 at 4:39pm

Thanks Dave.

Let me see if I understand your explanation.

I have an aim point on my target and fire 20 rounds.

I establish the coordinates of each round on an X and Y coordinate. The Average of each of these two coordinates give me the Mean point of impact.

Then I measure the distance of each shot from the Mean point of impact to get a mean distance. This mean distance is the figure of merit.

Is that correct?

Title: Re: Mean figure of merit.
Post by dbm on 11/17/05 at 7:53pm

That's how understand it! I'm just having trouble finding a contemporary reference with a definitive explanation.

David

Title: Re: Mean figure of merit.
Post by tjshooter on 11/17/05 at 8:38pm

David
Try the Textbook of small arms 1929 Page 239 with the additional fact that group size is 3.5 times the figure of Merit page 67.

TJ.

Title: Re: Mean figure of merit.
Post by 303smle on 11/19/05 at 3:11am

It appears, in the US at least, that the Mean Radius is not the same as Figure of Merit. The following is from Hatcher�s Notebook, pages 412 and 413.

Mean Radius is the average distance of all the shots from the center of the group. It is usually about one third the group diameter.
To obtain the mean radius of a shot group, measure the heights of all shots above an arbitrarily chosen horizontal line. Average these measurements. The result is the height of the center of group above the chosen line. Then in the same way get the horizontal distance of the center from the vertical line, such as for instance, the left edge of the target. These two measurements will locate the center of the group.
Now measure the distance of each shot from this center. The average of these measurements is the Mean Radius.

Figure of Merit. A method adopted by the Ordnance Department in 1923 for evaluating very small groups. It is obtained as follows: Draw a vertical line through the lowest shot in the group, also through the shot furthest to the left. Add the distance from the bottom lines to the highest shot to that from the vertical line to the shot furthest to the right. Divide by two.

I don't know whether the above Figure of Merit is the same as that used for the Mean Figure of Merit cited in the Treatise of Ammunition-1887. It seems there should be some British reference material that covers this.

bob c

Title: Re: Mean figure of merit.
Post by DoubleD on 11/19/05 at 2:36pm

Bob C,

Our discussion last week on the way to the range made me think more about this term "figure of merit" and that I really did not know what it meant.

Then this week my copy of The Treatise on Ammunition 1887 arrived and there was the term "mean figure of merit" as the standard for accurracy of Martini Henri ammo. Now I definitely had to know what it meant.

The fellows here had the answer, but I wanted a definitive reference, just to be sure.

Hatcher!!!! Why didn't I think of that. I had checked Mann and Greener but I couldn't find anything their work. I don't know why I didn't think of General Hatcher, that is no brainer.

This morning when I saw your post I went to my library and started looking. You know all those pretty fancy leather bound books I have been getting from The NRA Classics Firearm library, well they turn out to be more than just pretty faces.

Volume II of Whelen's Small Arms and Design and Ballistics explains the process with illustrations. And it is just as everyone here has described.

Thanks Gents.

Bob, start loading ammo, lets go to the range next weekend. I have to see if I can load better than 9"-40.

Douglas

Title: Re: Mean figure of merit.
Post by DoubleD on 12/03/05 at 11:14pm

Went shooting today and decide to apply the measurments to see what I have. I was testing a Nitro for Black load using a MHCC with a Parker Hale tang mounted peep sight.

Here is the 50 yard 12 shot group I got. Greatest spread ctc is easy, 4.825

http://www.fototime.com/0B76F09B6816C46/standard.jpg

Time for mean radius.

303smle wrote:

It appears, in the US at least, that the Mean Radius is not the same as Figure of Merit. �The following is from Hatcher�s Notebook, pages 412 and 413.

� � � � � Mean Radius is the average distance of all the shots from the center of the group. �It is usually about one third the group diameter.
� � To obtain the mean radius of a shot group, measure the heights of all shots above an arbitrarily chosen horizontal line. �Average these measurements. �The result is the height of the center of group above the chosen line. �Then in the same way get the horizontal distance of the center from the vertical line, such as for instance, the left edge of the target. �These two measurements will locate the center of the group.
� � Now measure the distance of each shot from this center. �The average of these measurements is the Mean Radius.

This is a bunch of work to calculate, but I finally came up with 1.8 inches mean radius.

Then following these instructions and then checking my own copy of Hatchers I tried to compute figure of merit.

Quote:

Figure of Merit. �A method adopted by the Ordnance Department in 1923 for evaluating very small groups. �It is obtained as follows: �Draw a vertical line through the lowest shot in the group, also through the shot furthest to the left. Add the distance from the bottom lines to the highest shot to that from the vertical line to the shot furthest to the right. �Divide by two.

I drew the verticle line through the lowest shot.
Then I drew a verticle line through the left shot.

The next step doesn't make sense.

Quote:

Add the distance from the bottom lines to the highest shot to that from the vertical line to the shot furthest to the right.

That's what is says in the book also.

What?

Title: Re: Mean figure of merit.
Post by 303smle on 12/04/05 at 5:39pm

What can I say? Hatcher must have had a bad hair day when he wrote that definition as it is obviously flawed.

I did a Google search on "figure of merit ammunition" and found at least six responses that resulted in a definition. Although they are all worded somewhat differently, the one closest to Hatcher's description is: To find it [figure of merit], draw a line through the center of the lowest shot in the group and then measure the vertical distance to the center of the highest shot in the group. Do the same with the shot farthest to the left and measure to the farthest right shot. Average these two measurements.

It is interesting that Hatcher's Notebook was first published in 1947 and has been through at least three editions. Mine is the third edition and you'd think someone would have noted the error by now.

bob c

Title: Re: Mean figure of merit.
Post by DoubleD on 12/04/05 at 6:22pm

Just like we thought.

Figure of Merit for the target is 5.11 we can do better.

Title: Re: Mean figure of merit.
Post by DoubleD on 12/06/05 at 1:49am

Found it in the Treatise of Ammunition 1887 Plate XI.

Bob's description
Quote:

To obtain the mean radius of a shot group, measure the heights of all shots above an arbitrarily chosen horizontal line. Average these measurements. The result is the height of the center of group above the chosen line. Then in the same way get the horizontal distance of the center from the vertical line, such as for instance, the left edge of the target. These two measurements will locate the center of the group.
Now measure the distance of each shot from this center. The average of these measurements is the Mean Radius.

The range is 500 yards.