A test of Shotmarker accuracy for long range BR.

[Dave M.]

Some suggestions based on my testing:

Reduce your impact velocity. If you can get your loads to pass through the target at, say, 1600 fps or less, and come in with some angle (like from the apogee of a long-range shot), it will show you more about the limitations of open-mic systems at long range.

What you are doing right now is nearly the ideal situation for the target to show accuracy (high-velocity impact). As the mach number of the projectile reduces, the shock wave the target is hearing is released farther and farther from the target, which gives the wind more time to shift the sound toward the downwind side and slight computational errors to become measurable.

Are you saying if Evan’s study was conducted at 1000 yards, the results would be much worse??

 

[Dave M.]

Thanks for the test. But your title says "for long range br" So now off to long range testing to see if errors multiply. Not sure why you are worried about wind. That is a real world condition.
You did show they are not accurate enough for short range br. Their groups are often smaller than the error.

Because wind moves the sound wave in the downwind direction. The move wind you have the further SM could potentially record impact error from the actual impact.
Dave

 

[RubiconJoey]

As someone who has never used any kind of e target, this is quite interesting and a bit eye opening. I had assumed that they were a bit more accurate than what your test suggests. Thanks for putting in the work; I'm sure it was tedious.

 

[Evan]

I shot my new 22 PPC today at 500yds and measured the Shotmarker vs paper again:

Strong headwind today, 15mph with gusts of 30+. Shotmarker says bullets came through at 2106fps on average, just for reference. The mean absolute error of these shots is 0.129" and a standard deviation of 0.108".

If you're interested in what the paper looked like:

22 PPC and 222 for 1000yd BR

I have two barrels coming, one for each of my Bordens, that I am going to be experimenting with this year. One is a 22 PPC and the other is a 222. Both are being throated out to 0.100" to get this kind of a seating depth for the 90 SMK: Left to Right: 22BR, 22PPC, 90SMK, 222 all at a "touch"...

forum.accurateshooter.com

 

[jelenko]

Nice piece of work!

 

[Cochran]

Has anyone tested the velocity readings of a shotmarker ? Would I be correct to assume the error in velocity readings would be about the same as the error in shot placement. Worse if the winds blowing

 

[Keith Glasscock]

Has anyone tested the velocity readings of a shotmarker ? Would I be correct to assume the error in velocity readings would be about the same as the error in shot placement. Worse if the winds blowing

The velocity readings are, well, assumed inaccurate (because they are a bit spastic). My observation is that on a range with only one shooter firing, The data is much better than when adjacent targets are receiving rounds simultaneously.

Back to your question: The velocity is, best of my ability to determine, measured by the difference in arrival time on the two microphones on each corner independently. From that, I would say that the physics of velocity indication errors are not driven by wind, but instead by echos and bounced sounds around the target.

Looking a little deeper, the target has to know the speed of sound (M=1.0) and the velocity of the projectile in order to calculate the shot placement. The mach number of the bullet defines the angle of the shock cone, and that determines how far away the bullet was when the sound the microphone heard was generated. From there it becomes simple-ish Pythagorean math with multiple equations.

In other words, measured velocity error drives shot location errors. It is one of several known causes of E-target mislocation of shots.

 

[Keith Glasscock]

I shot my new 22 PPC today at 500yds and measured the Shotmarker vs paper again:
View attachment 1531137
Strong headwind today, 15mph with gusts of 30+. Shotmarker says bullets came through at 2106fps on average, just for reference. The mean absolute error of these shots is 0.129" and a standard deviation of 0.108".

If you're interested in what the paper looked like:

22 PPC and 222 for 1000yd BR

I have two barrels coming, one for each of my Bordens, that I am going to be experimenting with this year. One is a 22 PPC and the other is a 222. Both are being throated out to 0.100" to get this kind of a seating depth for the 90 SMK: Left to Right: 22BR, 22PPC, 90SMK, 222 all at a "touch"...

forum.accurateshooter.com

Since this is a test for Benchrest, how did the group sizes fare? I think Min, Max, Mean, and SD of error in group size would be an interesting set of statistics.

 

[jelenko]

echos and bounced sounds around the target

How would these change the arrival time of the shock wave from the bullet?
Wave interference would change the amplitude, but not the speed, yes?

 

[Keith Glasscock]

How would these change the arrival time of the shock wave from the bullet?
Wave interference would change the amplitude, but not the speed, yes?

The reflected sounds travels farther, and arrives later.

 

[DirtySteve]

Just got my shot marker set up and calibrated. I can not wait to test the group accuracy. I had to put the boards on the front and back to get the angle correct for where I will be shooting from. Very sturdy frame.

 

[Dave Way]

I’m glad to see the interest in actually testing the accuracy of these systems in real world applications. I’m fine with a system being adopted so long as it is at least as accurate as measuring paper. From what I’ve seen, we aren’t there yet but threads like this serve to educate both the shooters and manufacturers as to where we are and where we need to get to.

Dave.

 

[chkunz]

Just got my shot marker set up and calibrated. I can not wait to test the group accuracy. I had to put the boards on the front and back to get the angle correct for where I will be shooting from. Very sturdy frame.
View attachment 1532438

Great!
For your accuracy testing do not forget that your calibration which aligns the SM virtual target with the paper target will not be perfect. The delta X and Y is shown on your calibration screen and must be accounted for in your accuracy comparisons. They are some other errors in measuring the paper coordinates that will need to be considered.
Best wishes,
Clyde

 

[Evan]

Since this is a test for Benchrest, how did the group sizes fare? I think Min, Max, Mean, and SD of error in group size would be an interesting set of statistics.

The measured groups from my previous post show similar error to the positional error of individual shots in that region of the target:

ShotMarker Groups​	Measured Groups​	Difference​
0.74​	0.547​	0.193​
1.80​	1.915​	-0.115​
1.04​	1.086​	-0.046​
1.82​	1.930​	-0.11​
2.68​	2.650​	0.030​
3.11​	2.753​	0.357​
4.41​	4.420​	-0.01​
1.67​	1.930​	-0.26​
1.20​	1.108​	0.092​
​	Mean Absolute Error:​	0.135​
​	St.Dev:​	0.108​