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

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.

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.

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.

Originally Posted by Micky Duck

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

..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.

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

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.

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.

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?

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"

Gold, best thing I've read on here today

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.


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:


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