Accuracy of Electronic Targets

[chkunz]

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

Chart 5, page 48 in NACA Report 1135 is an example of this and as you say method of characteristics is needed for something other than a point source. You see the simple equation sin =1/M in a lot of introductory books and it is good for learning the concept but is only good for a point source.

 

[243Mendoza]

Chart 5, page 48 in NACA Report 1135 is an example of this and as you say method of characteristics is needed for something other than a point source. You see the simple equation sin =1/M in a lot of introductory books and it is good for learning the concept but is only good for a point source.

Agreed. Most people, including engineers and scientists not versed in fluid mechanics and aerodynamics, don't understand that sin(mu)=1/M is only valid for an infinitesimal point source and not the shock angle of an object in a supersonic stream.

 

[diego-ted]

I was there, and my last match was against Brett Solomon who kicked my azz and put me out fair and square. Before doing so, our target missed FIVE of my shots and one of his IIRC. We had to switch targets. Do you think a puller would have missed five shots? Highly doubtful, and I've had some shitty pit service in the past. That being said I don't let pulled targets or Etargets keep me at home. I understand the downfalls of both going into a match......in my estimation Etargets aren't good enough for Nationals, State, Regionals or records.

you have an issue with your target! I have never seen 5 missed shots in stable conditions. Now I have seen accuracy issues rarely. YMMV.

 

[dskogman]

Here is a test I did today at 1000 yds. Six 5-shot groups over a period of about 50 minutes with a center hold for all. I did make some slight elevation changes so the groups did not overlap as much. the wind wasn't much (3/4 MOA max) but you can see the overall error increases as the wind picks up but the relative error within a group is not as much.

 

[F-CLassInfo]

Here is a test I did today at 1000 yds. Six 5-shot groups over a period of about 50 minutes with a center hold for all. I did make some slight elevation changes so the groups did not overlap as much. the wind wasn't much (3/4 MOA max) but you can see the overall error increases as the wind picks up but the relative error within a group is not as much.
View attachment 1339654

So in realty, out of 51(?) shots, only one would have changed score?

 

[dskogman]

So in realty, out of 51(?) shots, only one would have changed score?

That is correct. The error's hardly ever change the score due to statistical probability. More often an X will get changed because there is a smaller area with more shots particularly at 300 and 600 yds.
This test was done in mild conditions so the relative error is pretty small in a short string and doesn't affect much. As the wind speed goes up the errors become more erratic and the effects more pronounced at least at my range.

 

[F-CLassInfo]

That is correct. The error's hardly ever change the score due to statistical probability. More often an X will get changed because there is a smaller area with more shots particularly at 300 and 600 yds.
This test was done in mild conditions so the relative error is pretty small in a short string and doesn't affect much. As the wind speed goes up the errors become more erratic and the effects more pronounced at least at my range.

Nice. Just wanted to make sure I was following right.
Does the error always follow wind direction? Maybe that has already been touched in and I missed it.

 

[davidjoe]

Nice. Just wanted to make sure I was following right.
Does the error always follow wind direction?

Really good question. To my thinking, if you were to be pushed hard left, in flight, by a strong gust from the right, the sound wave of your bullet hitting the left microphones would arrive sooner than otherwise, (and longer to the right ones) compounding the shot’s tendency to physically hit left, because of the wind.

 

[TylerFromMS]

Literally just watched a target get pulled 3 times and come back up with the spotter marked as 3 (large) 9s. Scored as 10s.

Human error is real. I assure you they won’t admit it was an error.

 

[Ringostar]

This is when the score keeper needs to be paying attention and say to the shooter. Hey that sure looks like a 9, I think that the puller forgot to move the scoring disc. An honest shooter would agree. I had this happen once, however the score keeper didn’t calmly comment to me. Instead he started yelling challenge on whichever target that I was on. I got pissed! Not that I shot a 9, but if he would have just said Hey. I would have agreed, let him mark it a 9 and continued. However, now I had to wait while they pulled the target down and wondered why I was challenging it.

 

[TylerFromMS]

@Ringostar but it don’t happen like that. I heard “well I don’t agree with it but I have to mark it”.

Generous 9s on target 5! Keep in mind, this is what I saw when I was half ass looking up the line on rest period. Who knows the real count?

 

[jelenko]

From that pic, the spotter looks real close to the outer 9 ring.

 

[TylerFromMS]

From that pic, the spotter looks real close to the outer 9 ring.

Blow it up. The blob in the center is X/10. Scope out of focus due to mirage watching. Better yet, look at 6 (scored correctly) vs 5

 

[lawman29]

From that pic, the spotter looks real close to the outer 9 ring.

You're looking at #6 (scored an 8), the target in question is #5 scored a 9 looks like a 7/8

 

[jelenko]

You're looking at #6 (scored an 8), the target in question is #5 scored a 9 looks like a 7/8

Ah. I was was off by at least a ring.

But, then the shot wasn't close to a 9 - just an error by the target puller?

 

[243Mendoza]

Really good question. To my thinking, if you were to be pushed hard left, in flight, by a strong gust from the right, the sound wave of your bullet hitting the left microphones would arrive sooner than otherwise, (and longer to the right ones) compounding the shot’s tendency to physically hit left, because of the wind.

No, the bullet will always be in at the tip of the shock unless, it is slow enough to have a normal shock where the shock is slightly in front of the bullets or the bullet tip is blunt.
Also the bullet will align with the wind and so the shock will be aligned with the bullet.

 

[243Mendoza]

Here is a test I did today at 1000 yds. Six 5-shot groups over a period of about 50 minutes with a center hold for all. I did make some slight elevation changes so the groups did not overlap as much. the wind wasn't much (3/4 MOA max) but you can see the overall error increases as the wind picks up but the relative error within a group is not as much.
View attachment 1339654

It seems the calibration if off since the paper target and e target rings do not match ?

 

[TylerFromMS]

Ah. I was was off by at least a ring.

But, then the shot wasn't close to a 9 - just an error by the target puller?

Correct! Simple mistake. No ill intentions. However, I saw it multiple times when I was watching mirage on my rest period and when I was shooting. This, of course doesn’t count when I was in the pits are pulling.

Usually shooter/scorer didn’t really say anything. I said something when I was shooting and a competitor was getting very generous 10s that were spotted well into the 9 ring I saw in my spotting scope. I counted that phenomenon 3 times before I said something.

I’d rather trust a computer that doesn’t get fatigued rather than a human.

 

[F-CLassInfo]

@Ringostar but it don’t happen like that. I heard “well I don’t agree with it but I have to mark it”.

Generous 9s on target 5! Keep in mind, this is what I saw when I was half ass looking up the line on rest period. Who knows the real count?

View attachment 1343510

That is a 600 yard target and is a 7. Not even close to a 9.

 

[Albany Mountain]

Here is a 300 yard target I shot two years ago. As some rocket scientist will point out, there is some offset but consistant and not enough to change score.