SD at the target

[Bob3700]

Our shooting team consists of four shooters and we practice on a shot marker at 600 yds. We look at velocity and SD at the target between 308, 6 BR , and 223.
From multiple shooting sessions, we have found that the 308 delivers the lowest ( single digit) SDs and the 6 BR and 223 hover in the 10 to 15 area. This data comes from the shot marker program.
It would appear that the smaller the case, the more difficult it is to get into single digits at the target.
SD at the muzzle is one thing but SD at the target brings in an additional group of variables, the weather and of course the bullet itself.
On a given day, we are all shooting thru the same atmospheric conditions, so that affects all the same.
Just curious what u all have seen in this area. Our ammo is loaded using similar processes, cases wt. selected, powder weighed to a single kernel, bullets sorted by bearing surface and pointed and soft seated.
Just curious what SD numbers u all have recorded at 600 yds. For ur various cartridges.
I understand that the chrono numbers on Shotmarker are not calibrated but they do give u a value for comparison.

 

[Krogen]

Interesting subject! My buddies and I use a Shotmarker at 500 yds. I have gotten single digit SDs with 5 shot groups at the target with my 6x47 Remington. Admittedly, 5 shots is too small of a population, but it's an indicator. I have spent some time looking at the extreme velocity variations with QuickTarget to see how the variations relate to vertical stringing. Especially with slow, stubby bullets it doesn't take much ES (or SD) to string significantly.

 

[Ranger188]

What do the groups look like?
Is the 308's groups consistently smaller than the 6br and 223?
The whole goal is to consistently shoot the smallest groups at any distance
not the smallest SD

 

[dmoran]

@Bob3700
Great topic and very interested in your observations.
An aspect I am curious of is, how does the actual vertical dispersion of the POI's agree or disagree with the velocity data?

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[praveen]

Sharing this to get more insight into SD and why the data set should not be too small:

https://marketing.astm.org/acton/attachment/9652/f-f77f2c0b-9bdd-43c4-b29e-a5dc68c3a4b1/1/-/-/-/-/ja17dp.pdf

 

[RegionRat]

While there is nothing wrong with a study of the numbers out at the target as shown in the SM data files, the velocity stats to focus on would be the ones at the muzzle if you are concerned with the quality of the reloading or the recipe. Velocity values and stats at the SM are a bonus, but are also not particularly accurate just due to the short couple of the microphone stands.

There are reasons for a study of both sets of stats because noisy values can be from different causes, but the interior ballistics will be indicated by the values at the muzzle while the target value can be affected by the stability of the BC and winds, as well as wind effects on the microphones. (And not to mention the concept of under sampling, but simultaneous readings of muzzle versus target can be enlightening.)

If for example the bullet isn't flying well due to the twist, internal defects, or external damage, the values down range will increase in SD noise. Winds have an effect on the bullet's flight, as well as the opportunity to buffet the microphones of the SM.

On days with high winds, there can be a conflict between the muzzle, the SM stats, and the results on the target. On other days, there can be a long distance correlation between poor vertical and the SM stats as well as the muzzle stats.

By watching the differences between the muzzle values and SM values on windy versus calm days, you can get an idea of the effects of windy days on the SM.

By watching the difference in the muzzle versus SM on calm days, you can get an indicator of possible bullet stability issues.

I wouldn't get too excited about the SM data unless you first see problems with the vertical components of the groups or problems with the DOPE not tracking. YMMV

 

[ballisticdaddy]

I had compared the ES and SD using a LabRadar at muzzle to the numbers shown on the Shotmarker shooting at both 600 and 1,000 yards and they never lined up.

 

[Ned Ludd]

In my hands, the velocity data from the ShotMarker are simply not reliable. At best, you might be able to formulate some very coarse observations, but don't expect anything like the solid data sets obtainable from a quality chronograph measuring velocity at the muzzle.

 

[Bob3700]

@Bob3700
Great topic and very interested in your observations.
An aspect I am curious of is, how does the actual vertical dispersion of the POI's agree or disagree with the velocity data?

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Don,
The string of fire is twenty shots for record slow prone with irons. The groups of all three cartridges will exhibit waterline elevations n the score is as good as ur hold. The higher SDs show up at 1K where the vertical is more visible.
For our prone with irons, the SD variations don’t seem to make

What do the groups look like?
Is the 308's groups consistently smaller than the 6br and 223?
The whole goal is to consistently shoot the smallest groups at any distance
not the smallest SD

Don,
Any of the cartridges will shoot high X count cleans. Prone with irons is a matter of how well u are seeing that day!
Elevation issues become more visible at 1 K , at 600 the groups hold waterline elevation on all calibers.

 

[mgunderson]

Interesting topic and observations. I have looked at a pile of information from a larger group of shooters all shooting similar calibers over the course of several days. I arrived at the following conclusions:

Some people are better reloaders. You can see differences in the averages and SDs.

Fishtail winds can show up in the data.

Watch out for differences from one unit to the next. I was unable to split this out and poke at it more.

It is easy to draw the wrong conclusion from a small set of data.

Downrange SD is not the same a muzzle Sd.

I hope this Helps in some way.

 

[Dave Way]

Assuming identical conditions, ES and SD’s the difference can only be attributed to external ballistics once the bullet leaves the barrel. I’m going to say that you are witnessing bullets with more consistent ballistic coefficients holding their lower SD’s down range.

Dave.

 

[AAA]

This is just my recent data from the Missouri State F-Class match this last weekend shot on Shotmarker targets.
Different target number on stage 4 of day one, and on day 2
Each can decide whether it has any usefulness.
I don't know my MV or MV SD.
Rifle 6mm BRA
4-20 shot stages Saturday and 3-20 shot stages Sunday
Unlimited sighters on 1st stage of the day and 1 or 2 convertible sighters on other stages.
Very slight quartering headwind Saturday, a little more switching Sunday forecast less than 8mph
Maximum elevation of shots on any target was 3/4 MOA
Interesting how much velocity increased throughout the day.

Stage - SD - Score - Vel. @ target - # shots including sighters
1 - 6.3 - 200-15x - 1913 - 30
2 - 9.2 - 200-15x - 1935 - 21
3 - 7.6 - 200-15x - 1933 - 20
4 - 9.5 - 199-10x - 1974 - 20

5 - 9.2 - 200-14x - 1951 - 29
6 - 20.0 - 199-13x - 1975 - 20
7 - n/a - 199-14x - n/a - 22

I missed getting a picture of the last target before leaving the range so don't have SD or velocity data for it
Two 9s were near corner shot hold errors and one was a waterline hold error

 

[RegionRat]

Good shooting either way @AAA

Without the data at both ends, the muzzle and the SM, it isn't easy to show the issues.

When our club was Beta testing the SM, we took lots of data at 600 yards on calm and windy days.

We played with different target frame construction, but the target carriers were the window weight style where the frames slide up and down. The point is that the rigidity of the target frame and the carrier style have an effect on the quality of the score accuracy as well as those reported velocities, based on winds.

A shaky target on a windy day has an effect on the SM data when tested side by side with one that is held rigid in the same wind. But even then, wind has an effect on the SM performance regardless of the rigidity of the system.

By observing the muzzle data, at the same time as the impact and velocity data, you can tease out some performance issues, but without a doubt it takes some experience to estimate how much attention to pay to the SM velocity data and having the muzzle at the same time is necessary. YMMV

 

[mikecr]

Was distant SD adjusted from muzzle SD?

 

[Dave M.]

I am consistently getting single digit SDs on my dasher, girlfriend’s dasher and my 284 win. I would disagree with your assessment that it is easier to get single digit SDs with the larger rounds. Was all the ammo loaded by the same person and in the same manner? I doubt it and therefore what you are really seeing is who is likely making the best ammo. Also, I truly take the SD info at the target with a grain of salt. The shot marker system wasn’t designed or intended to provide perfect velocity info at the target. Location of bullet hole was the intention, not velocity. But, clearly you understand that based on your original post. Personally, I’ve never found it harder to achieve single digit SDs with our dasher cartridges.
To be clear, I shoot F open class and when I’m talking single digit SDs, it’s for 20 shot record strings.

Dave

 

[Dave M.]

Assuming identical conditions, ES and SD’s the difference can only be attributed to external ballistics once the bullet leaves the barrel. I’m going to say that you are witnessing bullets with more consistent ballistic coefficients holding their lower SD’s down range.

Dave.

Problem is you are assuming they are all starting with the same ES and SD at the muzzle and I’m fairly certain that isn’t the case. Without having the data at the muzzle, comparing SD data at the SM is virtually meaningless. Just my two cents.
Dave

 

[Ned Ludd]

This is just my recent data from the Missouri State F-Class match this last weekend shot on Shotmarker targets.
Different target number on stage 4 of day one, and on day 2
Each can decide whether it has any usefulness.
I don't know my MV or MV SD.
Rifle 6mm BRA
4-20 shot stages Saturday and 3-20 shot stages Sunday
Unlimited sighters on 1st stage of the day and 1 or 2 convertible sighters on other stages.
Very slight quartering headwind Saturday, a little more switching Sunday forecast less than 8mph
Maximum elevation of shots on any target was 3/4 MOA
Interesting how much velocity increased throughout the day.

Stage - SD - Score - Vel. @ target - # shots including sighters
1 - 6.3 - 200-15x - 1913 - 30
2 - 9.2 - 200-15x - 1935 - 21
3 - 7.6 - 200-15x - 1933 - 20
4 - 9.5 - 199-10x - 1974 - 20

5 - 9.2 - 200-14x - 1951 - 29
6 - 20.0 - 199-13x - 1975 - 20
7 - n/a - 199-14x - n/a - 22

I missed getting a picture of the last target before leaving the range so don't have SD or velocity data for it
Two 9s were near corner shot hold errors and one was a waterline hold error

This is not unlike the ShotMarker velocity data and statistics I have observed during matches. On the surface for a single match, they might appear to be reasonable. However, do you really believe your load velocity changed 61 fps as shown in red between the 1st and 4th strings? That would seem rather remakable. On numerous occasions I have observed velocity values for Varget loads that didn't change at all vary by 50, 75, 100 fps, or even more between strings on different targets. Not surprisingly, few of the values given by the ShotMarker at a particular distance matched those predicted by JBM at that distance using a known muzzle velocity, bullet BC, and atmospheric conditions. In other words, the velocities at the target face weren't off by a little bit, they were off by a LOT. If the velocity values themselves are off, how can the statistics derived from them be meaningful? So even though the numbers within a given string may appear realistic, this begs the question of how meaningful such data and the statistics really are. I certainly think they can be solid, but I also think they be off markedly, and it is difficult to know when and by how much.

For example, the data from my own personal ShotMarker seem to jive very well with JBM predictions. However, I am very considerate of the treatment I give the unit and how it is maintained and routinely calibrated. I have no way of knowing how the units used at matches at various ranges are treated, although I expect they likely receive harder use than my own ShotMarker, simply due to the frequency and volume of use, if nothing else. Further, one has to consider the variablility in the crosswind component at the target face in terms of measurement reliability. As I understand it, varying crosswinds at the target face can noticeably affect the velocity output. As such, I question how much useful information can really be gleaned from these data. I'm not trying to tell anyone whether to use e-target velocity data, that is up to the individual. But if one does decide to use it in some type of analysis, just be aware of the potential caveats.

 

[Bob3700]

I am consistently getting single digit SDs on my dasher, girlfriend’s dasher and my 284 win. I would disagree with your assessment that it is easier to get single digit SDs with the larger rounds. Was all the ammo loaded by the same person and in the same manner? I doubt it and therefore what you are really seeing is who is likely making the best ammo. Also, I truly take the SD info at the target with a grain of salt. The shot marker system wasn’t designed or intended to provide perfect velocity info at the target. Location of bullet hole was the intention, not velocity. But, clearly you understand that based on your original post. Personally, I’ve never found it harder to achieve single digit SDs with our dasher cartridges.
To be clear, I shoot F open class and when I’m talking single digit SDs, it’s for 20 shot record strings.
View attachment 1476374
DaveView attachment 1476375View attachment 1476378

Dave,
I am loading all of the different cartridges using the same equipment, processes, and components. The results are the same weekend after weekend on my own personal SM system. There may be a minor variation in the SD of each cartridge, example: the 308 on one weekend will be 7.2 while the next weekend it will record 9.0 for the same bullet and powder charge in the same wt. and make of cases. Primers the same lot. Same results for the 6BR and 223.

Knowing the SD at the muzzle might be interesting information, but I am shooting all of these rifles in different calibers on the same SM system on the same day. So the comparison of SDs at the target would seem to be at least a fair comparison.

The 308 is always single digits, the 6BR hovers around 10 and the 223 will consistently be in the 15-18 bracket. Each rifle will hold waterline elevation on the 600 yd target.

I am not assuming they are all starting at similar SDs at the muzzle, but the 600 yd spread would at least tell you that a similar difference in SD at 600 yds would also translate at the muzzle. That is discounting the effect of atmospherics on the bullets flight. I realize that the actual SD numbers are not calibrated or correlated, but the side-by-side comparison has to be valid.

All of this shooting is from 30-32 inch 5R rifled bbls, shooting prone with sling and irons. Not that the method of shooting should make any difference.

It is just an assumption that any variation in components tends to make a much smaller difference in a larger case vs a smaller one. The 308 is consuming 46 gr of powder in a 174 gr brass case. The 223 is 24 gr.(same powder) in a case that weights half the 308. So it would follow that weighing the powder charge to a single kernel would affect the SD of the 223 more than the 308.

The above is just my observations.

 

[Bob3700]

This is not unlike the ShotMarker velocity data and statistics I have observed during matches. On the surface for a single match, they might appear to be reasonable. However, do you really believe your load velocity changed 61 fps as shown in red between the 1st and 4th strings? That would seem rather remakable. On numerous occasions I have observed velocity values for Varget loads that didn't change at all vary by 50, 75, 100 fps, or even more between strings on different targets. Not surprisingly, few of the values given by the ShotMarker at a particular distance matched those predicted by JBM at that distance using a known muzzle velocity, bullet BC, and atmospheric conditions. In other words, the velocities at the target face weren't off by a little bit, they were off by a LOT. If the velocity values themselves are off, how can the statistics derived from them be meaningful? So even though the numbers within a given string may appear realistic, this begs the question of how meaningful such data and the statistics really are. I certainly think they can be solid, but I also think they be off markedly, and it is difficult to know when and by how much.

For example, the data from my own personal ShotMarker seem to jive very well with JBM predictions. However, I am very considerate of the treatment I give the unit and how it is maintained and routinely calibrated. I have no way of knowing how the units used at matches at various ranges are treated, although I expect they likely receive harder use than my own ShotMarker, simply due to the frequency and volume of use, if nothing else. Further, one has to consider the variablility in the crosswind component at the target face in terms of measurement reliability. As I understand it, varying crosswinds at the target face can noticeably affect the velocity output. As such, I question how much useful information can really be gleaned from these data. I'm not trying to tell anyone whether to use e-target velocity data, that is up to the individual. But if one does decide to use it in some type of analysis, just be aware of the potential caveats.

Ned,
My thoughts on the SD/velocity variations you have experienced could be attributed to the change in temps from the early morning start of the match and the last shots fired in the heat of the afternoon. You could begin with air temps in the high 60s and end the day in the low 90s. That might not account for 100 fps but certainly contributes to an increase in velocity simply due to density altitude. Also, variations in the actual bullets themselves would affect the the "At the target" numbers.
I agree that the velocity and SD numbers generated by the SM system are probably not accurate, but at least if you are shooting on the same target, you can compare the numbers from different calibers. The variation should be relatively consistent across a 20 shot string of fire.

Bob

 

[AAA]

This is not unlike the ShotMarker velocity data and statistics I have observed during matches. On the surface for a single match, they might appear to be reasonable. However, do you really believe your load velocity changed 61 fps as shown in red between the 1st and 4th strings? That would seem rather remakable. On numerous occasions I have observed velocity values for Varget loads that didn't change at all vary by 50, 75, 100 fps, or even more between strings on different targets. Not surprisingly, few of the values given by the ShotMarker at a particular distance matched those predicted by JBM at that distance using a known muzzle velocity, bullet BC, and atmospheric conditions. In other words, the velocities at the target face weren't off by a little bit, they were off by a LOT. If the velocity values themselves are off, how can the statistics derived from them be meaningful? So even though the numbers within a given string may appear realistic, this begs the question of how meaningful such data and the statistics really are. I certainly think they can be solid, but I also think they be off markedly, and it is difficult to know when and by how much.

For example, the data from my own personal ShotMarker seem to jive very well with JBM predictions. However, I am very considerate of the treatment I give the unit and how it is maintained and routinely calibrated. I have no way of knowing how the units used at matches at various ranges are treated, although I expect they likely receive harder use than my own ShotMarker, simply due to the frequency and volume of use, if nothing else. Further, one has to consider the variablility in the crosswind component at the target face in terms of measurement reliability. As I understand it, varying crosswinds at the target face can noticeably affect the velocity output. As such, I question how much useful information can really be gleaned from these data. I'm not trying to tell anyone whether to use e-target velocity data, that is up to the individual. But if one does decide to use it in some type of analysis, just be aware of the potential caveats.

Ned:
As mentioned in my post I was just posting info generated by the shotmarker targets at the match.
61 FPS is a big increase from match 1-4. As I mentioned we had to change targets after match 3 from target 18 to target 21 due to 18 not recording shots at the start of match 4. This change of target may have had an impact on the variance? I did not have to click down on the scope going to match 4.
Also on Sunday shooting on a different target.
I'm not making any judgements on the data reported as I have no idea how accurate it is.
What is important is I don't have elevation issues and can shoot tight tens and high Xs in good conditions.
An SD of 6 with the other third of shots being flyers causing elevation issues is not helpful to winning.