Assessing resulting vertical spread from ES (or SD) for your load at distance

How are the long range shooters amongst us determining the vertical dispersion that results from a given ES (or SD) at distance in their loads ?

It is clear that if using the usual shooting apps for this that the sight height should first be set to zero, and the zero distance also set to as close to zero as possible, as this approximates a horizontal launch. Then the difference in drop (from the horizontal) for variations in entered muzzle velocity will be correctly translated into vertical POI change as would occur in practice for ES variations.
If on the other hand the usual zeroing distance of 100m or 200m is entered into the ballistic app instead for this type of simulation, then the reported change in the vertical point of impact for a given variation in MV will be reduced, since the angle of launch is recalculated each time to match the zero distance, rather than being held constant.

I know this may sound a bit cryptic, but anyone who has looked into this will probably know what I mean.
So what method/s did you use?

….. a worked example:

Let’s say a bullet is being used with an average muzzle velocity of 2800 ft/sec. The ES of the load in that particular rifle is known to be ± 10 ft/sec, and the interest is in the maximum amount of vertical spread this could end up producing on a target at 1 kilometre.

The Applied Ballistics or JBM balllistcs calculator is set up with all the necessary inputs (including the usual zero distance of say 200m) and the drop is found for a 2800 ft/sec muzzle velocity. Lets say it is exactly 10 metres. Then the MV is changed to 2790 ft/sec (and 2810ft/sec, just to confirm), and new POIs at those settings are calculated and found to be say 70mm above and below the nominal. The ES is expected then to produce a 140mm spread on the target.

In fact the true dispersion from that size of ES is likely to be around ±85mm as follows: The calculations are repeated, except this time the zero distance is moved back in the simulation to as close to the muzzle as possible (ideally at the muzzle, but 1 metre may be the closest that can be entered). Because of the short zero it is necessary to also reduce the sight height to zero so the rifle doesn’t end up being tipped at a steep angle in the simulation. This then simulates a barrel held perfectly horizontally and where the bullet drops away below this line. More importantly with these settings the barrel remains in exactly the same position for both the 2800 ft/sec and the 2790 ft/sec and 2810 ft/sec calculations, giving a ±85mm difference in POI..
In the first example where the zero was 200m this is not the case: the barrel is simulated to launch the bullets at very slightly different angles for each of the three muzzle velocities, having the effect to partially compensating for the difference in MV.

The error using these ballistics programs to find vertical spread from ES becomes more pronounced the further out the zero distance used. Take an extreme example where the zero entered into the ballistics program is right out at the target at 1 km. The simulation will clearly calculate no change in the POI for any variations in muzzle velocity !

Your thinking way to hard about it, just go shooting

If your getting a large difference try factory ammo and see of it dose the same or buy a fancy crono


Sent from my SM-G935F using Tapatalk

One day when I grow up I hope I will be smart enough just to understand the question. Being able to add anything intelligent is just too much to wish for. I am very lucky I have a chum who understands this stuff so I don't have to.

Way over my head. But wouldnt an ES of +- 10 fps be an ES of 20?

Whats the question?

You technically should calculate all velocitys/ES at your zero range. E.g the ES at the target. Not impossible to do with the right chrono

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Originally Posted by longrange308

Your thinking way to hard about it, just go shooting

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" Long range shooting is all about limiting your uncertainties. The more variables you know and understand, the less you have to predict and the more certain you will be of impacting the target "

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Originally Posted by 199p

If your getting a large difference try factory ammo and see of it dose the same or buy a fancy crono

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Sound advice for shooters without a fancy chronograph or tight ES.

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Originally Posted by Gibo

Way over my head. But wouldnt an ES of +- 10 fps be an ES of 20?

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I like using the ALT+0177 keyboard shortcut (number lock has to be on)

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Originally Posted by PerazziSC3

Whats the question?

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Methods of determining the vertical dispersion at distance resulting from a given ES.


Perhaps of interest: back in the day I prepared a trajectory simulator in VisiCalc, Lotus123 or somesuch that started out calculating drop from the horizontal before adding in elevation for the zero distance (the formulas modelled published Sierra and Hornady data) so that would have been perfect for this sort of task.

Hi puffin, I really hadn't thought about this but it is true !

A better way to explore it would be to model a horizontal launch by setting the sight height to approx your own and specify a "zero offset" of exactly the same,using a short range . I'd use a zero range of 10m not sure why, dont trust percentage rounding errors which could get out of control at micro ranges orders of magnitude less than your working range eg drop difference over the ES could be like a mini fraction of a millimetre and just rounded out.

The answer Is Brian Litz Applied Ballistics Analytics program which will simulate hundreds or thousands of shots at working ranges using your specified ES (actually you input the sd). You do need a windows machine and it costs about $200 . In his book accuracy and precision he models the relative benefits of improving ES in several scenarios. He doesn't discuss the error you explained here when using standard ballistic trajectory programs but he must have dealt with it to get the analyses he wanted.

This is a good idea, I hadn't considered looking at it like this, I ushally just measure groups and worked off that.

Just played around with a online calculator ShootersCalculator.com | Ballistic Trajectory Calculator not sure how accurate it is but it let's you enter sight height at 0 and zero at 0.

For my loads with a maximum spread of 25fps it gives me a different point of impact of 1.3 inches at 500, which is somthing to think about , maybe we should be using the bottom number of ES or lower third instead of average to build drop charts, as I would ushally prefer to have point of impact slightly high than low.

If i built my drop charts off my avg velocity i would be .78inch low (20mm) @ 500 if my load was at the bottom of my ES. Not to much really at 500y, but I could see it being interesting at 1000y, could easily be a miss depending on target size.

I guess the goal is to keep ES down.

its all there in "the sharpshooter" written years and years ago...... and they used four rifles from memory to try it out. mind you back then 50fps variation was very good and they were still shooting deer out to 600 yards.

ASSUMING you are shooting a 3 shot group at the same speed and another at same speed and using group centres to get the -/+ 85mm it MIGHT make sense BUT if you are using single rounds to make calculations you arent taking into account any verticle error that normal group size will add /subtract to the maths....go shoot something LOL

I'm guessing that's a book? I am unfimiliar with it, I googled it and came up with a 22lr reloading tool, didn't know that existed, I'm learning lots today. :thumbsup:

also reading your first post again it doesnt matter stuff all if barrel is level or not the AMOUNT of drop or the difference between shots will be the same no matter what angle barrel is on within reason......like 45 degrees is obviously going to be different to 90 degrees but 5 vs 10 wont be buggerall as increase of gravitational pull will be so small as to be unmeasurable.

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Originally Posted by rusl

I'm guessing that's a book? I am unfimiliar with it, I googled it and came up with a 22lr reloading tool, didn't know that existed, I'm learning lots today. :thumbsup:

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sharpshooter was considered the "bible" for longer range shooting of game and getting rifles to behave back in the day... Matt and Bruce Grant are the authors. it still worth a read as it contains many truths which people seem to forget.

Couldn’t be bothered reading everything on here but sight height is the measurement from the center of the barrel bore to the center of the scope bore. Usually somewhere between 1.5-2”.
Zero range will be your sighted in range ie 100m. The bullet intersects a zero at two points if set at 100. Approx 25 it heats up and over the line of the cross hair and 100 it’s back down through the cross hair. From there all adjustments are up.
Type in muzzle velocity because it is what it says, velocity at the muzzle.
If the app doesn’t line up adjust your BC till it does.
I don’t know about all the other crap you were on about.
Above is how the apps were designed to work.
KISS

Sorry my answer maybe way off. I read your post a few more times and it just seems like too much coffee.

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Originally Posted by Bagheera

Hi puffin, I really hadn't thought about this but it is true !

A better way to explore it would be to model a horizontal launch by setting the sight height to approx your own and specify a "zero offset" of exactly the same,using a short range . I'd use a zero range of 10m not sure why, dont trust percentage rounding errors which could get out of control at micro ranges orders of magnitude less than your working range eg drop difference over the ES could be like a mini fraction of a millimetre and just rounded out.

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Phew.. finally someone who understands the issue. As you indicated, ultimately it comes down to a shooter understanding how their exterior ballistics simulator might be using the input data to calculate the outputs - then the situation you've raised where accumulated rounding error might cause a blow out can be avoided. A few minutes spent testing some carefully chosen boundary conditions can give insight into what is going on behind the scenes, and so this type of thing can possibly be worked around. Anyway, it is understood; for this method of predicting dispersion from ES we need to find a way to keep the simulated launch angle unchanged for small variations in MV.

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Originally Posted by Micky Duck

its all there in "the sharpshooter" written years and years ago......

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..and it is a very good book too. See how the subtitle is "How to get the best out of rifles and ammunition" ? No mention about getting the best out of exterior ballistics calculators though, which is kind of what this thread is about.

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Originally Posted by Micky Duck

ASSUMING you are shooting a 3 shot group at the same speed and another at same speed and using group centres to get the -/+ 85mm it MIGHT make sense BUT if you are using single rounds to make calculations you arent taking into account any verticle error that normal group size will add /subtract to the maths....go shoot something LOL

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I understand what you're saying here, and what the ballistics calculator is being used for is to predict just the contribution to vertical that the ES alone will make.

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Originally Posted by Micky Duck

also reading your first post again it doesnt matter stuff all if barrel is level or not the AMOUNT of drop or the difference between shots will be the same no matter what angle barrel is on within reason......like 45 degrees is obviously going to be different to 90 degrees but 5 vs 10 wont be buggerall as increase of gravitational pull will be so small as to be unmeasurable.

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Again I agree; the shape of the trajectory remains substantially unchanged for small variations in barrel angle from that at which the trajectory was calculated....

(Sigh) What it comes down to is that I've tried to describe an issue that can arise when using ballistic calculators to perform a particular assessment, clearly not very well as it turns out. It is of little consequence, and is of interest to very few forum members after all.

I've also been on this forum long enough to have come to realise that expressions such as "Go shoot something" and "Your thinking way to hard about it" or "overthinking this" are - grammatical errors aside - idioms for "I don't have a fucking clue what this thread is about but really feel the need to have my say regardless", and surely no one would want people to think that of them?

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Originally Posted by Puffin

I've also been on this forum long enough to have come to realise that expressions such as "Go shoot something" and "Your thinking way to hard about it" or "overthinking this" are - grammatical errors aside - idioms for "I don't have a fucking clue what this thread is about but really feel the need to have my say regardless"

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Gold, best thing I've read on here today :thumbsup:

Have you emailed Bryan Litz or asked the question online (AccurateShooter) ? He is a member there and seems to reply when asked questions like these. Would be interesting to see his response.

Taking a slightly different tack, as someone who has been dealing with the practical realities of limiting vertical spread... In my experience ES is far less of an issue in determining actual vertical spread on the target than shooter error. Unless you go to a machine rest setup that eliminates the shooter, it would be extremely hard to get conclusive results.

Also remember that there is not a direct correlation between MV and strike height on the target. If you have a barrel that is tuned or one that compensates positively due to natural harmonics, you may well find that slower MV shots impact higher...

Too true on both points Eben. So here is what I plan to do: lug around the Labradar and record every long range shot from now on AND use the TargetCam to identify and tie POI to MV for each shot as I fire them off, then I can go back and remove the theoretical ES contribution and see just how poor a shooter I really am from what is left - at least in a vertical sense !
I'm hoping on the second point you raised that a combination of low ES and the heavier barrel profile will minimise that to the point where it can be considered negligible. To date I haven't identified anything in the 6.5x47 other than a smooth rise in POI up the target with increasing MV. Perhaps it would be nice to have some sort of whipping node to base my preferred loads around, but I haven't found a significant one yet in the current set-up.
As for emailing, my original post had one method of getting the ballistics programs to output the correct information, and Bagheera came up with an alternative input method, so I believe we are sorted for now.

Are your groups ushally higher or wider?

Just a thought as the width of the group is most likely shooter/rifle error and the height would be shooter/rifle error plus ES velocity error, by that way of thinking if your groups are wider or square I don't think the velocity spread would be an issue worth to much time.

Just a thought, my groups are ushally like a triangle or if a high round count it's fairly circular which would indicate that I'm not getting great vertical spread from the load, if you had a consistent big vertical oval though it may be somthing to investigate further.

I'm no great shot but trying to look at this analytically.

Here is Brian Litz's book where he looks into the relative contribution of several uncertainties like wind, MV variation and rifle/shooter grouping capability.
Attachment 92940

He looks at several scenarios, corresponding to a typical shooter without special gear/under stress, a good shooter with MOA capability and fair windreading skills and an excellent shooter with 0.5 MOA gear and super wind skill to see who would benefit from controlling each variable like muzzle velocity. He uses standard deviation because it's tractable mathematically (Root sum of squares) but roughly the ES for 95% of shots will be 1.96 sdx2. So an SD of 10 fps corresponds to 19/20 shots being in a range of +/- 20fps.

He then simulates 1000 shots with a variety of MV, wind and other errors and sees where they land, then calculates hit probabilities for various sizes of targets. His program AB Analytics can do this with whatever uncertainties you choose, ranges or MV, BC etc you pt them in. I can't get out the nice graphics he has but it seems to work OK.

Here are his simulations showing the benefits of reducing variations in MV for a hypothetical Palma type .308:
Attachment 92943

He doesn't look specifically at how much MV ES contributes to elevation spread. Since you're summing squares, it wouldn't be much until you can shoot 0.5 MOA, which is why people intuitively say "just go and shoot a deer". But of course looking at these curves the F class competitor will never shoot MOA (say around 10" dia) at 800 yards unless you have SD around 10 fps (and if your SD is 20fps, you will only be able to do 1.5 MOA at 700 yd, other things being equal). You can also see that, for someone planning to shoot tahr at 500yd, MV SD doesn't start to make a difference; even 20fps SD doesn't reduce hit probability for the 10" target. It will be shooter grouping, range uncertainty and wind that are the limiting factors.

ok then...I dont have a fucking clue what you are raving on about other than trying to reinvent the wheel and suggest octagonal is better than round....better????
if your -+ 85mm is with single shots only it means fuck all......if its nice tidy 3 shot groups of say 10mm or 1/2" and a series of groups are 85mm apart you might be getting somewhere but single shots only proove rifle goes bang.

There are two issues here. 1. How much vertical movement will small velocity changes move you bullet at range. Change the velocity in your Ballistic app to reflect the max and min velocity at say 1000m and see what the app says that's the theory of it. I noted David Tubb running an off the barrel Magnetospeed at the King of 2 mile to gauge velocity changes and shot placement. 2)

Bagheera that's a good looking book, he has broken some basic information into a real world example, might have to get that one as well, any others guys could suggest.

I get the needing to zero the sight height and scope to zero in the calculator to work out ES caused by velocity as when you just change velocity the calculator alters where it thinks your sights will need to be so you arnt really seeing your true vertical spread of shots.

I think there is something here you are trying to figure out, in how the calculator works out the answer, somthing about rounding errors, I didn't catch it, it's over my head but I am interested in hearing what you find out so please put up your answers if you ever figure it out,

looking at your shown page 74.......you shouldnt be shooting animal past 700 yards at all, so anything past that is a moot point is it not????
rusl.....that explanation makes sense...it goes back to Sarvos thread re sighting in a short range........ MOST HV rifles cross line of sight at around 26 yards to give 3" high at hundy.....so in your calculation IF you used sight in range of 26 yards the figures would be pretty darn close to real time......

Sight in at 100 yards aiming for 1/2 inch or better for 3 shots. Check bullet drop at 400, 500 & 600 yards (my absolute max for hunting). Off we go hunting! Then after all that fu#king about end up shooting a deer or two under 100 yards and come home.

He's not talking about hunting (as in Matt and Bruce Grant's "The Sharp Shooter" book) not even long range hunting . This is for 1000m F class competition and longer.

The first book to get is Brian Litz "Applied Ballistics for Long Range Shooting"
Books/Library - Applied Ballistics LLC

Ahh got you.

Puffin, heres a link to an article that might interest you.
How Much Does SD Matter? - PrecisionRifleBlog.com