Testing E Target Accuracy

[GSS]

I have no doubt the NRA is going to have to rely on help from the folks developing this technology in order to come up with anything meaningful as far as test criteria goes. Judging from the current version of ShotMarker, I'd have to say it sure looks like it was thoroughly evaluated for accuracy of the results, and I wouldn't be surprised if Adam had some thoughts on the subject... same with the Hexta and Silver Mountain guys.

The back and forth discussion on 'acoustic center' and 'calibration' may have left some confused and questioning the suitability of e-targets in competition settings, so I thought an e-target screenshot along with a photo of the actual target might be useful for understanding why having an acoustic center that corresponds exactly with the center of the target isn't essential for accurate scoring.

First, the ShotMarker screenshot...
View attachment 1101500

...and the paper target that provided the aiming point.
View attachment 1101501

Notice the correspondence is very close, but not exact, and indicates the acoustic center of the ShotMarker is ever so slightly high and maybe a hair left (S2 and 3, illustrate this well). But even if acoustic center had been off by a larger margin, the same score would've been registered, assuming the shooter compensated accordingly (i.e. "My shots are landing high, thus I need to aim lower.").

Excellent Post,
Great illustration of how that system is every bit good enough for what we do in United States of America; Sanctioned NRA and CMP Matches.

If I were in the market for an E Target for myself or my club and I only read this thread for my research I would think no E Targets could be trusted..

I would also think they are very complicated and difficult to set up and use by the average person or Match Director..

With over 1000 ShotMarkers sold in the 1st year and around 600 Solo's that is obviously not the case.

In this thread I am also often confused about what systems and vintage of technology is being discussed in most of the posts.

There will always be the few (some anonymous) that greatly enjoy discussing the minutia of the science into eternity. There is nothing wrong with that and if they enjoy that better than shooting more power to them - imo.

The DOWN SIDE of all this tecchy discussion it is it RAISES DOUBTS about the "Current" technology for many,,,,, while many of us others will be out on the range enjoying the benefits that E targets provide them.

Many new NRA National Records were just shot on open sensor targets down at the Orange Blossum Regional in Florida. http://www.orangeblossomregional.com/match-scores/

When the commitment is made by a club to go to E targets and once the match is underway all that matters and all the shooters make sight corrections off of is what they see on the tablet.

What shows up for shot value on the tablets is all that matters...
Nobody will be in the pits checking each shot and the targets will not be sent out to NASA to compare what is on the dry or wet paper targets that were blowing around in the wind that day.

All on the range that day will have shot under the same conditions. The better shooters that most often won on paper targets will still win on E Targets. Just like at OBR recently where the new National records were shot.

Cheers,
See you on the range
George

 

[Bindi2]

cameras are good for lots of things but checking targets is not one of them. Use a plot overlay sheet for that.
We all like records just make sure the system that recorded it is up to the task in all conditions every day of the year.
Just think about it some countries and shooters are light years in front of you with E Ts. If you don't get it right from the go it maybe too hard and costly to fix.
The shooters have no option but to believe the monitor. I do now. There was a time when I didnt because they showed unbelievable shot groups. The ground swell grew to the point it took over and started the process to correct the issues from which we learnt more about ETs and the differences between open and closed systems. The road to success is rough the enemy tough. There is a place for all the systems just get them in the right order.
Your journey has just started mine is off to enjoy some shooting on ETs that I know are in the right place.

 

[GSS]

They are not of a competition grade.

Bindi2 (Name?)

I respect your opinion but you clarify a few things for me?

Am I correct to assume that you are not "currently employed or affiliated in any way" with the NRA or the CMP in the United States?

If you are employed / affiliated in any way with either or both of these USA organizations ( especially as an E Target expert / Authority of any kind ) would you please share with us here exactly what that relationship is?

Are you on any sort of Official E Target Certification board in Australia?

You do not state who you are in your posts or your profile but you post many statements about extreme testing experience and knowledge of E targets.

Would you clear up who you are and what your Technical background is?

Have you ever tested the currently sold ShotMarker or SMT Solo Systems?

Have you ever Shot on the currently sold ShotMarker or SMT Solo Systems?

Thank You,
George Smith
www.nfga.org

 

[Crow]

What if the acoustic center had been off left or right by a larger margin and there was a complete wind reversal. Wouldn't the wind call for the reversal be affected? I can see where acoustic center on the vertical axis wouldn't be a big deal unless it moved during a match.

S2 wasn't far from being called a 9?

After thinking about it some more, I realized where you were coming from with your comment about the wind call on a reversal, and I see your point. Say the acoustic center is 2 moa left of the aiming point and a 2 moa wind from the right is blowing at 90 degrees... you'd need zero windage to be on target according to ShotMarker. If that same wind shifted direction 180 degrees, you'd need 4 moa of windage to be in the acoustic center....

Being 2moa off of acoustic center is a pretty extreme example though... I literally only used 3 shots to arrive at the 'delta' on the e-target screenshot posted above and it's pretty close. Of course, that'll probably change slightly next time I re-face the target, which I do every time I switch yardages. I've taken pains to make accurate placement of different repair centers as close to true center as possible, but you know how it is with glue and large pieces of paper....

With a close delta, I don't worry much about what the paper target says except as it relates to verifying the actual grouping of the shots. On the shot that was almost a 9 (S2), I trust I had a full and accurate moa of 10 ring on the virtual target, and even though it looked a little more solid on paper, it's the virtual target that determines the score of the shot. If I'd taken the trouble to get the acoustic center better aligned, or if I'd glued the target face perfectly, the two would've matched more closely. In my mind, it's sort of like the 'noise' you'd get from a wrinkled target face.

 

[sdean]

I think that Blindi noname person is really a closet preacher. He ain’t stopped yet.

Ps. I heard the Chinese were going to bootleg the Hexta targets and sell them for $499.99 and free shipping.

HAPPY EASTER

 

[Crow]

Excellent Post,
Great illustration of how that system is every bit good enough for what we do in United States of America; Sanctioned NRA and CMP Matches.

Thanks George.

I'm pretty high on e-targets too, and think the ShotMarker stuff (the only system I have any experience with so far) is ready for prime time. They bring enough benefits as is, whether they're perfect or not, and I think most will concede that manual pit service can be less than perfect too.

I do have a couple of reservations though, especially after listening to what our Australian bros have to say on the subject.

Number one is the importance of target frame integrity... can't have a lot of movement and the positioning of the sensors has to be accurate for good results. I've seen what I consider remarkable accuracy with my ShotMarker, but it's frame is only 4' x 6' (as big as I can fit in the back of my truck easily), heavy, and the sensors are meticulously spaced. I wonder if that same level of accuracy translates well to 6' x 8' target frames resting in your average target carrier (if there is such a thing as an average target carrier).

I also wonder just how significant the Doppler Effect is on an open design. I mean, the Hexta folks went to a lot of trouble to overcome it... I continue to search for evidence of it, but realize I may never see it on a 4' x 6' frame being used at 600 yds in generally mild conditions.

 

[Keith Glasscock]

That is what I was trying to describe. 2 moa is an extreme example, but how much is acceptable?

Variables I wonder about:

Replacing target faces and not getting them square or back in the exact place? Does there need to be a gage for this? Overkill? ( Yeah I know when we paste paper targets they aren't exact and can shrink and wrinkle with moisture, and probably come from the printer in varying sizes, but if any of that happens, you still know where the center is because it is, shall we say, x marks the spot.)

Wood target frames warping and/or expanding and shrinking due to humidity changes? ( these could be built out of synthetic material if this turns out to cause a lot of movement.)

Sensors being out of square? ( This is an installation issue, but does it need to be checked regularly on a wood target frame? How often? What is reasonable variation?)


And what I think might be the biggest concern, wobbly target carriers.

The question would be, how much do any of these variables change and is it enough to be significant? I don't know the answer, but I think it needs to be considered.

The variation in center location as a result of a change in wind across the face of the target isn't all that hard to rough estimate.

Thinking in 2 dimensions:
In a windless environment,a sound wave will propagate in a circle with a radius related to the speed of sound. The time to reach a sensor on the very corner of a 6 ft square target is close to .03771236 seconds from the center (using 1125 as the speed of sound).

If we insert a crosswind across the face, our nice, pretty circle becomes and egg shape. The sound is moving through the air at the same speed as before, but the air mass is also carrying the sound downwind with it.

If we calculate out the elliptical shapes (half upwind, taller than wide and half downwind, wider than tall), we can calculate the effective speed of arrival of the sound wave. In the case of a 5 mph wind, I guesstimate the change in geometric location would be roughly Correction - 0.235 inches at the water line. That number shrinks as the distance between sensors decreases. For a 3 ft square target, it is more like Correction - 0.12 inches.

The problem is that the effects of wind across the target face (even if my guesstimates are completely off) should be the same regardless of distance the bullet travels getting there. It should represent more noticeable effects as the range shortens because the error represents a larger percentage of a ring width.

I know that Adam has the math on this down to a science. Perhaps he will comment.

4/22/19, Corrected a math error.

 

[chkunz]

The variation in center location as a result of a change in wind across the face of the target isn't all that hard to rough estimate.

Thinking in 2 dimensions:
In a windless environment,a sound wave will propagate in a circle with a radius related to the speed of sound. The time to reach a sensor on the very corner of a 6 ft square target is close to .03771236 seconds from the center (using 1125 as the speed of sound).

If we insert a crosswind across the face, our nice, pretty circle becomes and egg shape. The sound is moving through the air at the same speed as before, but the air mass is also carrying the sound downwind with it.

If we calculate out the elliptical shapes (half upwind, taller than wide and half downwind, wider than tall), we can calculate the effective speed of arrival of the sound wave. In the case of a 5 mph wind, I guesstimate the change in geometric location would be roughly 0.47 inches at the water line. That number shrinks as the distance between sensors decreases. For a 3 ft square target, it is more like 0.23 inches.

The problem is that the effects of wind across the target face (even if my guesstimates are completely off) should be the same regardless of distance the bullet travels getting there. It should represent more noticeable effects as the range shortens because the error represents a larger percentage of a ring width.

I know that Adam has the math on this down to a science. Perhaps he will comment.

Keith,
We have a 1124 ft/sec sound wave and a 5 MPH crosswind which is 7.3 ft/sec. The distance from the center to the corner of a 6 ft target is 4.2 feet. I am able to visualize what you describe but am having trouble getting a 0.47 in change in geometric location as a result of the crosswind. I am not saying your calculation is incorrect but I am not able to replicate it with my visualization of the physics. Any suggestions?
Clyde

 

[GSS]

I was actually talking about not having the acoustic center lined up with the aim point center in the horizontal axis during set up or after a target face change. The example target posted up a little from this post shows the onscreen mark was to the left of the actual bullet hole on the paper. I am assuming this is meant to be corrected during the calibration.

What happens if the paper target is replaced and not lined up with the old target, like happens in the pits on manual targets? Does it need to recalibrated? Does this happen during a match? Am I missing the way this works completely? Totally possible.

I am past worrying about the accuracy of the target itself. I am asking more about the variation that might be seen in wobbly target carriers, target setup, target face change, target frame dimensional stability over time as relates to sensors moving, etc. Might be minor stuff and not matter.

I hope to shoot on mine next weekend. I am going to clear some of this in my own mind over time.

What I did with my Shotmarker frames to result in zero calibration / offset needed was simply;

Build the frames so that they are square.
Install the four magnetic sensor brackets square and equal distance apart in all dimensions.

Then back the inner lower screw out on each base enough to make an x with some string.
Where the 2 pieces of string intersect is the center. That is where you want the center of the X to line up on all targets you put on the frame.

I used coroplast as the face and cut 3' x 3' squares ( size of a 600 yard MR target) for the targets to get attached to. I drilled 1/4" hole in the dead center of the coroplast where the string made the X.
I then put 1/4 inch holes dead center in the 3'x 3' pieces of coroplast and put a golf tee thru both of them.
Then I made a c shaped frame / pocket where all the 3' x 3' centers will get slide into. One for the 200 yard SR target, one for the 300 yard target and one for the 600 yard target for each frame.

If you do all this correctly your 1st shots on the paper target will line up with what you see on the tablet with no zero / offset calibration required.

We run down to the pits between line changes and slide the new centers into the pocket with the proper size aiming black / target for the yardline.

For the 600 it's easy because the paper target is the same size as the 3 x 3 coroplast centers. For the 200 and 300 I make sharpie marker corners so even a monkey could staple the centers on to within a mm or 3 of dead center. Eventually the center gets shot out of the coproplast so you need to go by the marks on the corners.

It's so close nobody ever notices any difference in their zero's.
Nobody can see that good or hold that good to notice any difference. They simply adjust to the sighters and go on happily ever after. Once you are shooting all that matters or all there is to go by is what shows up on the tablet.

I am certainly not a rocket scientist and despite how some of the posts in this thread sound, luckily you don't need to be a rocket scientist to use an $800 ShotMarker E Target.

I have zero 1st hand experience with the Silver Mountain Solo but I would assume it is just the same as the ShotMarker.

We are very fortunate to have these two quality / affordable options to choose from.

 

[sdean]

What

We run down to the pits between line changes and slide the new centers into the pocket with the proper size aiming black / target for the yardline.

For the 600 it's easy because the paper target is the same size as the 3 x 3 coroplast centers. For the 200 and 300 I make sharpie marker corners so even a monkey could staple the centers on to within a mm or 3 of dead center. Eventually the center gets shot out of the coproplast so you need to go by the marks on the corners.

It's so close nobody ever notices any difference in their zero's.
Nobody can see that good or hold that good to notice any difference. They simply adjust to the sighters and go on happily ever after. Once you are shooting all that matters or all there is to go by is what shows up on the tablet.

I am certainly not a rocket scientist and despite how some of the posts in this thread sound, luckily you don't need to be a rocket scientist to use an $800 ShotMarker E Target.

I have zero 1st hand experience with the Silver Mountain Solo but I would assume it is just the same as the ShotMarker.

We are very fortunate to have these two quality / affordable options to choose from.

I like the sound of that. First time I heard of any paper record of the relay. I don't know what a Hexta target looks like but at Laurel usually the range never goes cold for the match.

 

[GSS]

I like the sound of that.
First time I heard of any paper record of the relay.

I don't know what a Hexta target looks like but at Laurel usually the range never goes cold for the match.

Clarification;
We don't keep any paper (target) records of anything.

3 relays shoot offhand and siting from 200 (on the same paper targets in the slots)
We go down and swap to the 300 yard aiming black while shooters are moving back to 300

All 3 relays shoot 300 rapid (on the same paper targets in the slots)
We go down and swap to the 600 yard aiming black while shooters are moving back to 600

All 3 relays shoot 600 (on the same paper targets in the slots)

We go down, put the frames away and ShotMarker electronics and tablets on the charging stations then go enjoy each others company for a sandwich and a beer while chatting about the triumphs and tribulations of the day.

No paper targets records are kept or used in any way.
What shows on the tablets after each shot or string is all that we refer to for anything.
We do use paper scorecards tho..

G-

 

[GSS]

How's this for an Aiming Point vs Optical Center offset?

Had heard of F Class guys complaining that on E Targets if they don't get a fresh face every time or often enough their aiming point gets blown out and makes their hold off's more difficult and their X count suffers.

I set up our E Targets like this with an F center high on a regular 600 yard center as a test in a 3 x 600 league match late last year.
The F Class guys loved it...

I'm a service rifle sling shooter and with my little 34mm 4x scope the F center high in the black was zero distraction for me.
I just put my reticle dot in the standard 600 yard target X Ring and shot my strings as always.

Thoughts ?
G-

These were temporary target centers we did last year out of cardboard on the 4 ShotMarker systems we bought mid year last year so we could use all 6 of the E targets we had then in the last two prone matches of the season to introduce people to the new E targets. We now have a total of 10 ShotMarkers and they are all set up with coroplast with pockets to slide the different centers into.

We wanted no cardboard so they wouldn't have to be rebuilt every time we get heavy rain during a match.

 

[Crow]

Thoughts ?

Cool idea, but it'd be easier to just raise (or lower) the vertical delta to move the acoustic center up (or down).

 

[sdean]

No paper targets records are kept or used in any way.
What shows on the tablets after each shot or string is all that we refer to for anything.
We do use paper scorecards tho..

G-[/QUOTE]

I did misunderstand. But thinking out loud if you had 30 centers made up before hand and an easy and precise method of changing them that would leave a paper record for a later review if someone was inclined. Might appease the Etarget bashers.

 

[GSS]

No paper targets records are kept or used in any way.
What shows on the tablets after each shot or string is all that we refer to for anything.
We do use paper scorecards tho..

G-

--------- sdean said -----------------
I did misunderstand. But thinking out loud if you had 30 centers made up before hand and an easy and precise method of changing them that would leave a paper record for a later review if someone was inclined. Might appease the Etarget bashers.[/QUOTE]
----- end sdean quote ---------------

In my opinion that would be too much extra work for Match Directors and would take away from key benefits of E targets.

Again IMO, 99% of the ET bashers will always be bashers.
Even if / when they are no longer actively competition they will continue to bash from a comfy chair on the interweb...

Hopefully not every range in their areas go to ET's.
This way, If they like pulling pits and paper targets they can keep pulling pits and paper targets.

The rest of us will move on making the best of the next step in the evolution of the sport / game.

 

[Keith Glasscock]

Keith,
We have a 1124 ft/sec sound wave and a 5 MPH crosswind which is 7.3 ft/sec. The distance from the center to the corner of a 6 ft target is 4.2 feet. I am able to visualize what you describe but am having trouble getting a 0.47 in change in geometric location as a result of the crosswind. I am not saying your calculation is incorrect but I am not able to replicate it with my visualization of the physics. Any suggestions?
Clyde

Hi Clyde,

To keep it from distracting from the discussion, I'll IM you the details of how I derived that number.

 

[chkunz]

Hi Clyde,

To keep it from distracting from the discussion, I'll IM you the details of how I derived that number.

Thank you so much, best wishes, Clyde

 

[Keith Glasscock]

I found a math error in my previous post. It has been corrected in the post.

Thanks to Clyde for helping me find my error.

 

[Pwc]

I don't understand all I know about this electronic scoring; has anyone put a camera in front of the target to record actual impact vs electronicly "derived" impact and check in real time?

 

[rardoin]

I don't understand all I know about this electronic scoring; has anyone put a camera in front of the target to record actual impact vs electronicly "derived" impact and check in real time?

Yes...photograph of target (started with a new face) compared to display during pit change; the shots on screen correlated as well as could be ascertained visually.