That is a good question ot was 4 years ago and I dont remember exactly. I didnt put that in there. I measured in mm then converted to inches in the calculation so I would guess to say it is 0.5mm maybe less as I would have estimated that.
Accuracy of Electronic Targets
- Thread starter goodi
- Start date
So to be fair to SMT you could have put a +/- that represents your estimate of your measurement error. Or you could have accounted for it in some way. I bring up this point because in my testing of a ShotMarker system, I estimated that my measurement error was a significant portion of the reported ShotMarker system error so I was reluctant to share my results because I was concerned that that point would be missed.
Alexander-M
Gold $$ Contributor
[Follow-up to my post #61 on this thread:]
Objective: To compare the shot locations per the ShotMarker (SM) X-Y coordinates provided by the SM CSV file with the corresponding shot locations on the actual paper target using the measured X-Y coordinates on the paper target.
Method: On the paper target, use a digital caliper to measure the distance from the center of the small hole made by the bullets, to the vertical and horizontal axes. The location of each shot was then plotted using the square root of the sum of the X and Y values squared. Using CAD, I plotted the results for both the SM displayed target and for the paper target.
A negative X value means the shot was left of the Y-Axis, and a negative Y value means the shot was below the X axis. Note that the largest error was 0.118”, and the smallest was zero.
The plot below indicates that my target center for SM should be adjusted slightly higher and to the left for better correlation of the SM shot locations with the actual shot locations on the paper target.
I built and calibrated my ShotMarker target frame in June 2019, started using it immediately afterwards, and have not recalibrated or checked calibration since then. I do not plan to recalibrate the target as the error is OK for my purpose. The frame is made of 1” (full one inch) x 3” oak, and the base of 2X4’s. It is rather sturdy. I always shoot at 600 yards with my SM target, usually shoot early in the morning when there is little or no wind, and have not experienced any problems.
Alex
PS: Note that in either case, Paper or SM, the score would be the same: 100-8X
Objective: To compare the shot locations per the ShotMarker (SM) X-Y coordinates provided by the SM CSV file with the corresponding shot locations on the actual paper target using the measured X-Y coordinates on the paper target.
Method: On the paper target, use a digital caliper to measure the distance from the center of the small hole made by the bullets, to the vertical and horizontal axes. The location of each shot was then plotted using the square root of the sum of the X and Y values squared. Using CAD, I plotted the results for both the SM displayed target and for the paper target.
A negative X value means the shot was left of the Y-Axis, and a negative Y value means the shot was below the X axis. Note that the largest error was 0.118”, and the smallest was zero.
The plot below indicates that my target center for SM should be adjusted slightly higher and to the left for better correlation of the SM shot locations with the actual shot locations on the paper target.
I built and calibrated my ShotMarker target frame in June 2019, started using it immediately afterwards, and have not recalibrated or checked calibration since then. I do not plan to recalibrate the target as the error is OK for my purpose. The frame is made of 1” (full one inch) x 3” oak, and the base of 2X4’s. It is rather sturdy. I always shoot at 600 yards with my SM target, usually shoot early in the morning when there is little or no wind, and have not experienced any problems.
Alex
PS: Note that in either case, Paper or SM, the score would be the same: 100-8X
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Before I released the results and how I was testing I talked with Wayne (at the time) and Daniel they were aware if what I was doing and were fine with it. But yes I should have included a plus/minus error and how I measured. But the overall point was and still is the error people complain about is minute.
Jeff Porter
Gold $$ Contributor
I guess what bugs me about some of this is the confusion about an offset either due to calibration or placing of the aming point (TARGET FACE) out of positon with the acoustic center versus an actual displacement of a shot from its actual path through the target. Unless you verify the target face is exactly in the acoustic center, you should not even look at the comparison of the two. Alexander and Shawn have done this and it compares to my observations ther will be a small deviation on some shots due to wind, shooting angle etc. but much of tht can be minimized by sturdy target frame construction.
None of the pictures comparing digital to paper by overlay show merely a uniform shift, though, that could be explainable by alignment adjustment. Differences can be found going in all directions.
If I were overlaying the two, I would scale the two images exactly to size, then transpose one over the other into the position where the center shots, in and around the X come closest to each other, on average, then press save.
That is an important point that you, Shawn, Alexander and I understand but most will not get it. For actual use the acoustic center does not need to match the paper target center perfectly and in fact it is sometimes advantageous to intentionally off set them. But for accuracy testing they need to be as near congruent as possible since any non congruency carries over into the error calculation and is not fair to the electronic target system. That is why I asked Shawn what his estimate of measurement error was because such an estimate needs to consider the non congruency.
This is why I did not widely share my test report because my estimate of this error in my test was a significant percentage of the ShotMarker error. If any of you that understand this would like a copy of my report send me an email at chkunz@bellsouth.net and I will send you a copy.
Ned Ludd
Silver $$ Contributor
As has already been noted, a uniform offset between bullet holes and e-target impacts can easily be caused by the target acoustic center and the target face center not being perfectly aligned. The purpose of overlaying the e-target impacts onto a paper target with bullet holes should be to align the two sets of holes as well as can be done, then to look for individual shots where the two impacts points still don't line up. A uniform offset where the majority of the paper holes and electronic impact points would actually line up pretty well if one or the other target was shifted slightly is merely an issue of misalignment between the paper target center and the e-target acoustic center. Such misalignment issues may be addressed using the "calibration" feature of the target.
The key point here is that there is a big difference between misalignment of the paper target center/acoustic target center, and poor accuracy of the e-target system. They are not at all the same thing. Unless one were to regularly overlay the paper target and e-target images, slight misalignment of the two might not even be noticed by the majority of shooters. This is simply because we can twirl our scope knobs to center our shots according to the e-target system readout. Because this is how the score is recorded, the actual location of the bullet holes in the paper target face don't really matter. What matters is where the e-target systems "thinks" the impacts were. What would be a problem is if one were to overlay the two target images (paper/e-target) and most of the holes/impacts line up perfectly (albeit with with some tweaking to account for any misalignment between the two target centers), except that there are a small number that do not line up at all. That would represent a clear difference between the points of impact as determined by the paper target and e-target; i.e. inaccuracy.
The key point here is that there is a big difference between misalignment of the paper target center/acoustic target center, and poor accuracy of the e-target system. They are not at all the same thing. Unless one were to regularly overlay the paper target and e-target images, slight misalignment of the two might not even be noticed by the majority of shooters. This is simply because we can twirl our scope knobs to center our shots according to the e-target system readout. Because this is how the score is recorded, the actual location of the bullet holes in the paper target face don't really matter. What matters is where the e-target systems "thinks" the impacts were. What would be a problem is if one were to overlay the two target images (paper/e-target) and most of the holes/impacts line up perfectly (albeit with with some tweaking to account for any misalignment between the two target centers), except that there are a small number that do not line up at all. That would represent a clear difference between the points of impact as determined by the paper target and e-target; i.e. inaccuracy.
The thinking behind looking at the center of each set of shots, digital and paper, is that peripheral shot sound waves are affected to a greater extent by the Doppler effect.
If one were to very nearly shoot the upper right mic in billowing wind, that mic would fire in almost exactly the same amount time later, as it would in dead clam. The opposing mics would not, though, as the wave traversed a moving mass of air the target cannot account for. ** That’s really a second, separate kind of effect, conceptually, from a center X shot shifting one direction in a moving mass of air that affects all microphones.**.
If one were to very nearly shoot the upper right mic in billowing wind, that mic would fire in almost exactly the same amount time later, as it would in dead clam. The opposing mics would not, though, as the wave traversed a moving mass of air the target cannot account for. ** That’s really a second, separate kind of effect, conceptually, from a center X shot shifting one direction in a moving mass of air that affects all microphones.**.
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Larry Koch
Silver $$ Contributor
I think some may be missing the point of digital anything. The winner of a match can be picked before the first shot is fired.
And that may be why e-targets haven't been approved by the NRA.
And that may be why e-targets haven't been approved by the NRA.
Warren Dean
Team Savage F-TR
Could you elaborate on that statement? It sounds as though you are implying something nefarious. 
.Shawn, I went back and checked the data from my report and the errors at 200/300/600 yards were essentially the same in inches considering my estimate of my measurement error.
I am not making a comment about the effect of distance on errors but the effect of firing line offset from the target line.
not quite true. A test that the Australians did many years ago show that errors with bullets with a strong shock (e.g. 6RSAUM with the Berger 180) were smaller than that shown with 80gr 223 bullets. That is because the shock wave from the 180gr bullet is stronger and steeper than the weaker and shallow shock generated from the 80gr 223 bullet and this difference becomes larger as the distance to target increases. So the difference in error may be small at 300 to 600yd but at 1000yd, the difference is significant. The shallow angle of the shock from the 80gr bullet would arrive at the sensors almost simultaneously and may give the impression that the shot is closer to the center than actually.
Based on my experience and understanding of shock waves, I do not believe this to be true, to arrive at the sensors simultaneously the bullet must be in the center of the target. The shock wave is three dimensional with a cone shape for a strong shock at Mach 2 and above and more of a bow wave as the bullet approaches transonic. Study the pictures of shock waves at various Mach numbers like those in "Modern Exterior Ballistics" by Robert L. McCoy and you will see what I am talking about.
If, in fact, the offset is consistent out to 600 yards and then increases at 1000 yards then something else is going on. It may be that we are just seeing variations within measurement error.
look at page 64 of McCoy. This shows a pic of bow shock off the nose of bullet at M-1.02. it is very close to a normal shock. As Mach number increase, the shock angle will steepen and etarget accuracy will increase.
Re: the Australian test, they did a rigorous test with respect to target placement and shot hole measurement. It is available on the web
Looking at various pictures of shock waves at various Mach numbers, I find it amazing that someone has used this physics and built such a useful tool for our sport.
I have read several of the Australian test reports including the one that you reference as well as reports by others. Some are good and some not so good. Data is always better than opinions but bad data is worth less. We used to say that bad data was worse than no data at all and that still holds.
Shock angle is a non-simple analytical function of wedge angle (or nose angle for bullets) and mach number. For more complex shapes such as bullets ogives with bearing surface , you need to use Method of Characteristics if you want an analytical solution. The etarget algorithms uses a much simpler approximate equation that use sin (mu)=1/M where mu is the mach angle. The mach angle approaches the shock angle as the mach number approaches M=1.
BTW, I find the Aussie tests to be the most rigorous tests that I have seen so far. These test were done to validate their use in their National and "state" matches. (as opposed to our NRA letting things slip by).
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