Question on SD. How many shot per group is sufficient?

I think it is very odd to say that a chrony doesn't matter at distance.

It is a well accepted fact that your drop changes as your speed changes. To say that speed does not affect vertical at distance is completely illogical.

If you had a load that had terrible SD/ES (and for the sake of this conversation lets say that you have a very reliable chrony/data/etc) the only way for it to have good vertical at distance would be that the barrel harmonics perfectly and consistently offset the change in drop cause by variances in muzzle velocity.

As BadAsMo stated above, David Tubb at the Ko2M had a mageneto speed attached to his rig. When he shot he would observe his impacts at distance and then check his velocity to see if he missed because of changes in velocity or some other factor (wind speed, bad trigger pull, etc.)

I would bet there is a very high correlation between good vertical at distance and good ES/SD numbers. There are some caveats to this though 1) being that you need a high quality chrono 2) You need a sufficient sample size to make sure your ES/SD is reliable

TL;DR A good SD/ES does not guarantee a good load, however, a bad SD/ES cannot equal a good load
 
What you suggest IS correct IF the load is already in the correct node for the barrel. Again, research positive compensation.... very old concepts that were proven effective nearly 100yrs ago.

With even the very best chronies, you have a mechanical error of around 5fps... What does that mean....

If you had an output for 5 shots registering 3000fps for all, the real velocity might be anywhere from 2995 to 3005 fps and the chronie couldn't tell the difference. There is a post in the reloading forum where a reloader is comparing a Chargemaster with an FX-120i. The chargemaster suggests all charges are the same BUT the actual weight varied... and it varied within the error rating of the Chargemaster. So although the chargemaster was working within design parameters, the error was larger then what many LR shooters need/want.

So the number crunching is limited by the error of the machined used for testing. Use the numbers as a reference... don't take it alone without comparing to the target at distance... hopefully, further then 100yds.

IF you could produce a chronie that was accurate to 1fps or less, THEN you have the mechanical precision to measure and report to single digit ES/SDs. It wouldn't be worth the cost to develop cause it wouldn't really help anyways... that target at distance is really telling all you need to know.

On the surface, the discussion with velocity makes alot of sense... I followed it myself. Fast bullets should travel quicker to target and thus drop less then a slower bullet. The faster bullet should land higher then the slower bullet. The larger the difference in velocity, the bigger the vertical spread at distance.

It all makes perfect sense and I completely agree IF, and this is a big IF, both bullets left the barrel at exactly the same point in its travel. Barrels vibrate as the bullet travels down the bore, it is not static. Problem is bullets don't leave the barrel in exactly the same point of its travel and this is what positive compensation is trying to discuss... and explains why bullets leaving with varying speeds can and do land in the same point downrange.

And if you accept this concept, you can then understand the error in depending on velocity in isolation.

I have tested using chronies, lab radars and electronic targets.. Yes, we have monitored velocities. yes, there is a correlation SOMETIMES for speed vs impact location. But because it is not all the time, you have to be careful in your assumptions.

In F class competition, EVERY shot is marked on a target so we know exactly where each shot landed. We shoot alot of rds each match so you have a very large sample size. By plotting the impacts vs the wind, we have a very good idea of affect on conditions to the impact of the bullet. We are indeed doing real world testing against our data.

Any competitor at 1000yds/900m has found out that small changes in powder charge weight can have significant affects on vertical dispersion at distance. The results can be multiple increases in vertical for charge weight changes as small as 0.1gr to 0.2gr in a mid sized case like the 308/284 win/ 6.5 creedmoor. I can assure you, you will not see a difference in velocities when adjusting powder charges that small... all the data overlaps

But you will know things are not right when you are bouncing up and down on the target. Why many, if not most, have gone to high end milligram scales. we need charge weight precision to +/- a kernel of powder.

My life would be a whole lot easier if I could tune with my magnetospeed and a target at 200yds... better yet, 100yds.

Jerry
 
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This has all been a very interesting discussion.

To get back to the OP though with his limited distance problem.

Shoot as far as you can but I would also highly recommend choosing a load that has good SD numbers (single digit is good). Do both at the same time if you can.

At 100M groups are good, at 100M groups and a chrony is better. A chrony and 1,000M would be great but that is not an option for everybody.
 
What seems to get confusing here as I read Jerry's comment above is the difference in vertical dispersion that is caused by velocity variation and the different point of impact (high low left right of wtf) that is caused by inconsistent barrel harmonics.

This enters the realm of paralysis by analysis for newbys....

In support of Ryans point that you cannot have great accuracy without a low SD/ES.... if you draw upon Jerrys point on barrel harmonics where barrel whip cycle is dependent upon muzzle velocity, you will have the best chance at hitting a consistent barrel whip node if the velocity spread is low and the velocity is tuned to the whip cycle that barrel seems to like.

So this gets back to the need for a chronograph so you can keep tabs on the velocity (at various temperature ranges BTW) and compare that to the point of impact as you search for that perfect load.

How you would do that blind is like swatting flies in the dark.
 
Mystic Precision said:
So a 3000fps reading is +/- 15FPS when it is working PERFECTLY. An ES of 30 is hard wired into the machine at this velocity. If the light varies, this can cause more error.

Some of the best chronies bring this down to 5fps... you can confirm the specs on the Oehler 35.. and new 2 chronie set up. What I am simply saying is the error of the machine may be higher then the numbers you are trying to crunch. Saying you have an ES of 10 when your machine can't do better then 30 is just fooling yourself.
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This has been an interesting thread for sure. The built in tolerances of the measuring equipment we all use, be it chronographs or scales, is a factor we must account for. Relevant to this discussion, the maker of the Auto Trickler now makes a Two-Box Chrono and claims the accuracy is within 1 fps. The price is cheaper than many high end chronographs like Labradar and Magnetospeed to mention a few.

I'm curious if anyone will be giving this a try and what kind of results they'll get.
 
BadAsMo said:
What seems to get confusing here as I read Jerry's comment above is the difference in vertical dispersion that is caused by velocity variation and the different point of impact (high low left right of wtf) that is caused by inconsistent barrel harmonics.

This enters the realm of paralysis by analysis for newbys....

In support of Ryans point that you cannot have great accuracy without a low SD/ES.... if you draw upon Jerrys point on barrel harmonics where barrel whip cycle is dependent upon muzzle velocity, you will have the best chance at hitting a consistent barrel whip node if the velocity spread is low and the velocity is tuned to the whip cycle that barrel seems to like.

So this gets back to the need for a chronograph so you can keep tabs on the velocity (at various temperature ranges BTW) and compare that to the point of impact as you search for that perfect load.

How you would do that blind is like swatting flies in the dark.
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Intuitively, this is bang on... however, way too many rifles I have shot DON'T behave this way. I have had rifles that grouped better at 250yds (and beyond) with loads that had larger SD/ES numbers (again, that goes to the positive compensation theory). The load tuning happens with powder charge and/or seating depth NOT by what the chronie suggested. Maybe the numbers were affected by the error in the chronie???? Either way, I don't take chronie data as gospel anymore... I care so little about this data, I don't record it anymore either... but I sure keep track of my charge weights and ammo specs and ambient conditions.

Again, I am not saying using a chronie is bad... a great tool to have BUT depending on the output data over plotting the target is not ideal.

I want very well shaped small groups at distance WITH decent chronie data. If you can shoot at 200yds, or further, test as far as possible. With careful load work up, the target will show you all that you need to know.. .back it up with chronie data to confirm if desired BUT the target will not lie.

Target shooters have been doing very well long before consumer chronies were even possible. The set up that has put me on the podium 3 times this year has never seen a chronie and I am shooting out to 1000yds trying to hit a 5" circle. I extrapolated my velocity based on charge weights and it put me on target so.... One day I will put on my magnetospeed and see what the output is but it really doesn't matter as it is working so well at distance.

If the 2 box chronie works as reported, it could help alot for those with limited range distance. However, I have done too much tuning at 1000yds varying charge in 0.1gr increment to know that even this chronie will have limited useage. Better.... should be. The final solution... I wish it were but I will continue to confirm and adjust my load at the furthest distances I compete at.

If there was an easier way, believe me, I would be using it.

FYI, I feel 250yds as a nice minimum distance if restricted at the range. Tune for vertical as low as possible as you approach max loads in published data. Use the chronie to show the velocity so you know when you are approaching max pressures... this is really where the chronie shines.

My rule of thumb for "good enough"... 1/4 MOA tall... 1/2 MOA wide. You are going to hit alot of targets way out there.

Jerry
 
luckey said:
Hi, a newbie question for the long range guru here. I am working on a load for 1000-yard steel match and wonder how many shot per group is sufficient to get a trustworthy SD and in what range the SD is accurate enough for this application? Thanks!
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On mid to long range steel, where scoring is hit-or-miss, you should be concerned with ES, not SD so much when tuning with a chronograph.

SD represents the range that most (2/3 or so) of your bullets are flying at. You don't really care about those. If your wind call and hold are good, you will hear a ding.

ES represents the outliers, which are going to help you miss. Even worse, if you call your shot on one of these and see the splash, you will make a bad dope correction.

If you insist on basing a 'good' load on SD, the more shots you record, the more you will wash out the ES outliers.
 
I think everyone here is saying the same thing but as we are males we are unable to concede.

Since you say you no longer care about ES/SD data how do you know your loads are not single digits anyways? Also, you do not define what a large ES/SD means?

All I am saying there is probably a very high correlation between good groups at distance and good ES/SD numbers.

I think doing load development just using distance is great (as you said the target does not lie). However, at distance, many more factors (such as shooter ability, wind, atmospherics) will come into play. I do my load development with an Atlas bipod, a rear squeeze bag, and a 3.5# trigger - I am an OK shooter. By relying on chrony a bit more than what some others do I can take some of the human error out of the equation. I could probably get a more suitable set up but prefer to spend my $$$ elsewhere.

I am not saying that a chrony replaces shooting at distance but it could maybe provide a tiny short cut if you don't have easy access to a 1,000 yard range.
 
Ryan.M.Anderson said:
I think everyone here is saying the same thing but as we are males we are unable to concede.

Since you say you no longer care about ES/SD data how do you know your loads are not single digits anyways? Also, you do not define what a large ES/SD means?

All I am saying there is probably a very high correlation between good groups at distance and good ES/SD numbers.

I think doing load development just using distance is great (as you said the target does not lie). However, at distance, many more factors (such as shooter ability, wind, atmospherics) will come into play. I do my load development with an Atlas bipod, a rear squeeze bag, and a 3.5# trigger - I am an OK shooter. By relying on chrony a bit more than what some others do I can take some of the human error out of the equation. I could probably get a more suitable set up but prefer to spend my $$$ elsewhere.

I am not saying that a chrony replaces shooting at distance but it could maybe provide a tiny short cut if you don't have easy access to a 1,000 yard range.
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Even with a very good chronie, magnetospeed or labradar, the error in the machine is similar to the numbers we are trying to crunch. So it really wouldn't matter what the output was. If someone was to try the new 2 chronie machine and compare to others, there could be a better understanding of the variations in the output.

Like the scale example in a previous post, it wouldn't matter how precise that reloader tried to keep the chargemaster output... the error built into the scale negates the value of that work. As was explained, maintaining perfect value on the chargemaster scale didn't provide precise powder charges in the pan.

The best we use so far is around +/-5fps (and these have been compared to the old gold standard which is the Oehler 35 which also gets down to around 5fps).... so the machine has an ES up to 10fps built into every shot... could be zero, could be up to 5fps above or below actual if the chronie is working perfectly. I know most want to take the screen output as perfect but that might not be the case.

If the chronie suggested one load was 8fps and another 18fps but the 18fps load shot flat and tight at 250yds and the 8fps load was tall and narrow, I would take the 18fps load.

That is what I mean.

Ball park...if I had an accurate flat grouping load at distance, but the data suggested as ES of 20fps or so with the generic Chronie, I wouldn't get too worried about it. What does the target show and then I would confirm further out

If you have a chronie that has an error UNDER 5fps, then you can start to focus more on what that data might indicate to you. The error in the machine has to be much smaller then the data you are trying to crunch. The 2 chronie suggested error of 1fps is very interesting... and sure beats the 1/2% of the consumer grade cheap stuff.

Without a place to test far, the very best chronie will be helpful BUT I would rather they invest in a high end milligram scales first.. THIS matters much more then any other measuring tool we use in reloading.

Jerry

PS, a caldwell Rock is around $100. good rear bags are around $60... these will last a lifetime of testing and give far more confidence in your groups which saves you time and alot of money. How much does it cost for each BANG nowadays? Get rid of human error as much as possible when testing.. excellent advice. The gear to do that doesn't cost much AND improves confidence in the results. If I do not have confidence to group my rifle at the level of accuracy I need to compete, what is the point of testing loads? what is the point of that chronie?
 
There's no doubt that the ultimate proof of a good load is how it prints on paper, but that needs to be statistical in nature.

One good group does not a good load make, especially at extended ranges.

There are so many outside variables that can contaminate feedback, such as mirage, wind, intermittent cloud cover, time of day and dumb luck.

Many deer hunters think every snap in the woods is a deer, and we must be mindful not to interpret the results the way we want them to be without considering what else might be contributing factors.
 
In regards to error in technology - chronies in particular. I do not think that they would read high on one shot and low on the next. It is probable that they would read consistently high or consistently low.

As Alpheus linked to up above I think the newer age chronographs (LabRadar & Magnetospeed) are accurate enough for what I am trying to do.
 
Alpheus said:
You mean like I did here? https://www.canadiangunnutz.com/forum/showthread.php/1483258-Magnetospeed-vs-Labradar-a-test
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Exactly.. and why I use, sell and recommend the magnetospeed. It works very well compared to the "best" we typically have access to. The Labradar works great and both compare very well to the Oehler. Costs and quirks aside, they are the best we have... until the 2 chronie gets out there and can be tested.

But this also illustrates the point I am getting at. Change out the device and it could be the magnetospeed reading faster vs another labradar. Ultimately, it wouldn't matter cause both machines are working within their mechanical error. The average difference of 4.5fps is bang on within their specs.

Their relative difference was very close and similar which again, a very good indicator of working properly and within spec.

When I am looking at this type of data, I discount the "ones" digit... so I would only be concerned that the velocity was 298X... I don't care what X is cause it could be distorted by the error of the machine. When you look at both machines without that final digit, they produced the "same" output within their error so the numbers actually overlap... excellent.

As far as the machines are concerned, they produced the same output.

Most importantly, if I entered 2980 or 2989 in a ballistics program, it isn't going to change my drop chart so I don't care what that final digit is.

Does it resolve the load tuning question? Of course not but it never was going to.

Jerry
 
Ryan.M.Anderson said:
In regards to error in technology - chronies in particular. I do not think that they would read high on one shot and low on the next. It is probable that they would read consistently high or consistently low.

As Alpheus linked to up above I think the newer age chronographs (LabRadar & Magnetospeed) are accurate enough for what I am trying to do.
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That is an assumption you can make but mechanical error is not consistent... if it were, it wouldn't be an error now would it. You will see the error rating of measuring devices in the scientific gear world. Any output within the machines rated error rating is the SAME value. You just have to get a machine with an error smaller then the data you are trying to create.

That Chargemaster has a built in error of +/- 0.1gr (some are up to 0.2gr)... If you trying to weigh your charges to the same 0.X gr, this is not the machine you want to use. The FX-120i has an error of +/- 0.02gr so at worst, it is still 1/2 the error we are trying to achieve. The output then is trustworthy for the accuracy we want but I wouldn't say my load weight was accurate to 0.0Xgr... I would say it was accurate to 0.Xgr

scores in F class have skyrocketed since these quality milligram scales have become SOP... when you can measure and tune to that 0.Xgr, you can control the vertical at distance and that keeps them in the X/V ring.

Will this matter to you or your type of shooting? I think that in field shooting, low vertical loads become far more important cause you have the added error of a wobbly shot and less then ideal data. If the ammo is already creeping towards the target size at distance, shooter error will have a far larger impact on result. When you are fighting error related to actual distance to target, affects of conditions and coarse scope adjustments, having loads with lots of vertical dispersion adds more headache to figuring out your LR dope.

things never get better when you increase distance to target.

YMMV

Jerry
 
So you sell the magnetospeed but won't rely on its results...

Edited to add: The Labradar states accuracy to 0.1% - at that level of accuracy errors would be irrelevant.
 
Ryan.M.Anderson said:
So you sell the magnetospeed but won't rely on its results...

Edited to add: The Labradar states accuracy to 0.1% - at that level of accuracy errors would be irrelevant.
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The magnetospeed works exactly as it was intended and that provides a valid velocity value to be used in determining your drop. There is no Chronie that is perfect for load tuning per se. I wouldn't use an Oehler either...

I rely on the velocity reading from my magnetospeed (or any quality chronograph) to make up a drop chart that works... and the magnetospeed does this very well.. This is why I use it, sell it, and recommend it.

For load tuning, I recommend the better milligram scales like the FX-120i which I don't sell.

As I have indicated from the start, I have found years back that chronie data is not ideal for LR load tuning....

Both the Labradar and Magnetospeed have similar error ratings... either can be used in the same way.. provide you with a valid velocity for the projectile.

The fact that the output data is being used for load tuning has nothing to do with what the machine was originally designed to do.

Test this for yourself. Make up some ammo that is 0.1gr higher or lower then your ideal load determined your way.. put that FX-120i you have to use. Shoot this over any chronie you want. I bet if you shot 10rds each and compared the output, there will not be enough velocity difference for you to go "AHA"... but the target at 250yds and further is going to show some dramatic differences.

Then shoot this ammo as far away as you can... compare the hit rates and where those bullets land. I bet you start to see some dramatic difference especially in the vertical location of the impacts.

Let us know how it turns out for you.

Jerry

Jerry
 
Jerry, I really think you are just skipping over part of the responses.

People are not saying that you can solely rely on chrony data to develop a load. They are saying they are a tool that can help.

I am not saying that your methodology is invalid. I am pretty sure (although I can only speak for myself) that people are saying there are benefits to using a chrony.
 
I have agreed all along with the utility of the chronie. It is just the application of the data that we differ on....

If you are building ammo for LR shooting, I have never found 100yds to tell the full tale regardless of what my chronie said. I have tested at 250yds and further and the groups ALWAYS told me the truth. Obviously, if you tested with the chronie you would see some decent output data BUT I have also seen times where the best data didn't produce the best results on target.

I try and work with a process that is 100% reliable over any rifle or chamber I want to test. If any step can vary, I modify its importance in how I use its data.

Good Chronies let me determine my drop very well. That is their use to me and how I use its data.

Good milligram scales, proper case prep, good supports while shooting and DISTANCE, help me fine tune loads that work as far as that bullet is going to fly.

By all means, use that chronie to help guide your tuning. But do test at distance as I have described so that you can see the chronie's limitation as well.

The OP is limited to 200yds and I have suggested to test at 200yds, not 100yds. The further you can test, with or without a chronie, the better your load tuning can become.

A good milligram scale is far more important then a great chronie wrt to developing great LR ammo....

Jerry
 
Ryan.M.Anderson said:
In regards to error in technology - chronies in particular. I do not think that they would read high on one shot and low on the next. It is probable that they would read consistently high or consistently low.
.
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I have considered this myself and devised a test to prove or disprove the reliability, but I shot my chronogragh before I could do it.

Just line up 2 chronies in front of each other and shoot through both with each shot and compare the values.

The results would illustrate if there are inconsistencies from one shot to the next or if each chrony is consistent but off by ### fps.

Now that I have a Labradar I lost interest is running this test but maybe some CGNer out there could do it and post the results.

If there is a certain randomness between them, you could probably average the two for a statistically more correct value.
 
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