Figure of Merit
10 November 2024 07:21 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
dime_novel_heroGoing shooting at a friend’s farm tomorrow. It’s going to be just plinking so there will be no analysis going on but it did have me thinking about how the Victorian’s measured their shooting. I remembered that YouTuber Rob at BritishMuzzleloaders had a video that covered it and rewatched a bunch of his videos looking for the one that I remembered. I relearned a bunch of stuff but couldn’t find the specific video I had remembered until I did a Google search.
Figure of Merit is a measure of mean radial distance of shots from the center of a group. Breaking that down, it is calculated by first averaging the X and Y coordinates of every hit to obtain the location of the center of the group. Then, you average the distance from that center to each hit.
As the video states, it was the method which the School of Musketry at Hythe, Kent used to establish military standards starting in 1853 and forward and, though it might not have been the best or most precise method of calculating accuracy, it was a quick and relatively easy method of doing so.
And it’s Victorian, so, the method I will use.
Going back to my outing of last month and the target it produced.
Ammo: Fiocchi factory loads, 45 Colt, 250 GR LANFP, 750 FPS, 40 rounds fired
Rifle: Rossi 92, Open sights, firing from sandbag
I didn’t keep the target but I was able to scale the photograph such that my graphics program could measure. I also had the useful advantage of having found one of Rob’s forum posts where he shared a copy of his spreadsheet. It was a matter of collecting the X-Y coordinates of each of the hits (I chose the hits in stages 1 and 2) and entering them in the appropriate fields and interpreting the results.
Figure of Merit at 100 yards = 3.16
So what?
Well, to understand any of that we need to do the analysis and comparison.
First, I had estimated using my Mark 1 Eyeball calculation that I was about 7 inches to the left and maybe an inch low. The spreadsheet’s Sight Adjustment fields confirm this with me being 6.92 inches off and .32 inches low. As I said in my previous post, this rough guess is sufficient for the question of capability I was asking at the time.
What does the Figure of Merit tell me? In isolation, not much. From the video, Rob’s example was 8.3” at 500 for a Parker Hale P58 Naval Rifle. The School of Musketry had established that, for the Enfield P53, a value 14-15” at 500 yards would be acceptable. Extrapolated out, my FOM would be 15.81” at 500 yards, nowhere near as good as Rob was shooting and just barely unacceptable for the School of Musketry.
These are very different rifles, however. Most importantly, the Enfield has a 39 inch barrel designed as a military battle rifle, with a full power charge to reach out to ranges on 600 yards. My Rossi 92 has only a 20 inch barrel and uses a pistol cartridge suitable for short ranges and hunting. Still, I think it’s impressive that the technology had developed such that a pistol cartridge out of a short barrel could almost compete in terms of accuracy with a muzzle loading battle rifle of only 40 years before.
The value of Figure of Merit will be more valuable to me, not in comparing different rifles but instead comparing my performance over time. Sure, I could do that with a scorable target with concentric circles but the spreadsheet also told me that, to correct my windage of 7” to the left I would need to move my rear sight 3/100 of an inch. The rear sight is just dovetailed in and I don’t have a precision tool to manage that. I would need to do something drastic like tapping it with a hammer and then going out and doing all the measurements again to see how I did.
Better to correct that with Kentucky Windage and focus instead on sight picture and firing consistently.
Figure of Merit is a measure of mean radial distance of shots from the center of a group. Breaking that down, it is calculated by first averaging the X and Y coordinates of every hit to obtain the location of the center of the group. Then, you average the distance from that center to each hit.
As the video states, it was the method which the School of Musketry at Hythe, Kent used to establish military standards starting in 1853 and forward and, though it might not have been the best or most precise method of calculating accuracy, it was a quick and relatively easy method of doing so.
And it’s Victorian, so, the method I will use.
Going back to my outing of last month and the target it produced.
Ammo: Fiocchi factory loads, 45 Colt, 250 GR LANFP, 750 FPS, 40 rounds fired
Rifle: Rossi 92, Open sights, firing from sandbag
I didn’t keep the target but I was able to scale the photograph such that my graphics program could measure. I also had the useful advantage of having found one of Rob’s forum posts where he shared a copy of his spreadsheet. It was a matter of collecting the X-Y coordinates of each of the hits (I chose the hits in stages 1 and 2) and entering them in the appropriate fields and interpreting the results.
Figure of Merit at 100 yards = 3.16
So what?
Well, to understand any of that we need to do the analysis and comparison.
First, I had estimated using my Mark 1 Eyeball calculation that I was about 7 inches to the left and maybe an inch low. The spreadsheet’s Sight Adjustment fields confirm this with me being 6.92 inches off and .32 inches low. As I said in my previous post, this rough guess is sufficient for the question of capability I was asking at the time.
What does the Figure of Merit tell me? In isolation, not much. From the video, Rob’s example was 8.3” at 500 for a Parker Hale P58 Naval Rifle. The School of Musketry had established that, for the Enfield P53, a value 14-15” at 500 yards would be acceptable. Extrapolated out, my FOM would be 15.81” at 500 yards, nowhere near as good as Rob was shooting and just barely unacceptable for the School of Musketry.
These are very different rifles, however. Most importantly, the Enfield has a 39 inch barrel designed as a military battle rifle, with a full power charge to reach out to ranges on 600 yards. My Rossi 92 has only a 20 inch barrel and uses a pistol cartridge suitable for short ranges and hunting. Still, I think it’s impressive that the technology had developed such that a pistol cartridge out of a short barrel could almost compete in terms of accuracy with a muzzle loading battle rifle of only 40 years before.
The value of Figure of Merit will be more valuable to me, not in comparing different rifles but instead comparing my performance over time. Sure, I could do that with a scorable target with concentric circles but the spreadsheet also told me that, to correct my windage of 7” to the left I would need to move my rear sight 3/100 of an inch. The rear sight is just dovetailed in and I don’t have a precision tool to manage that. I would need to do something drastic like tapping it with a hammer and then going out and doing all the measurements again to see how I did.
Better to correct that with Kentucky Windage and focus instead on sight picture and firing consistently.
