Ballistic calculators disagree with my actual elevation amounts - help please!

GrahamC · Jul 29, 2024

Hi all,

I have two rifles chambered in 6.5 Creedmoor (Ruger RPR and Accuracy International AT-X) both with Vortex Razor HD Gen 2 scopes. I shoot at a range with known distances from 100-1200 yards in 100 yard increments.

My rifles are zeroed for 100 yards and I have dope settings for 100, 200, 300 and 600 yards. I've tried a variety of different calculators (Hornady 4DOF, Vortex, several others). They all seem consistent in their come up values which don't match either of my rifles. For instance with the RPR at 600 yards they state around 12.8MOA come up while I have to actually dial 14.5 - a big difference! With the AI, the calculators state 1.35 come up at 200 yards when I actually have to dial -0.25 from my 100 yard zero.

I'm using a Garmin chrono so have accurate MV. I'm using Hornady ELDM 147gr factory ammo so know the bullet weight, am specifying barrel twist, sight height over barrel, temperature etc.

Is there an explanation why the calculators seem so far off vs my two rifles?

I want to shoot at 1000 yards and have no dope for that. How can I use a calculator to determine that? Should I change the bullet G7 BC to accurately match the come up at 600 yards and then use the 1000 yard figure the calculator then suggests?

All gems of experience welcome!

Thanks.
Graham

Eric32 · Jul 29, 2024

Are you using a kestrel by chance?

GrahamC · Jul 29, 2024

Eric32 said:
Are you using a kestrel by chance?

No, I'm not.

Hornday 4DOF on my iPhone. Garmin Xero chronograph for MV. Sight height measured with digital calipers. Factory match ammo.

Graham

Partsunavailable · Jul 29, 2024

In my opinion, you have some things to figure out before going out to 1000. With the AI at 200 yards, you don't have a good zero at 100. That's the only possible explanation.

Eric32 · Jul 29, 2024

Have you tried adjusting the drag factor on the 4 DOF

GrahamC · Jul 29, 2024

Partsunavailable said:
In my opinion, you have some things to figure out before going out to 1000. With the AI at 200 yards, you don't have a good zero at 100. That's the only possible explanation.

So I zeroed at 100 yards and then shot another 60+ rounds at target. Example of my results below, I think after about 40 rounds. What potential issues could I have with my 100 yard zero then, so that I have some idea of what to consider and eliminate?

GrahamC · Jul 29, 2024

Eric32 said:
Have you tried adjusting the drag factor on the 4 DOF

4DOF doesn't appear to have a drag factor. It does have an axial form factor but the max range of adjustment still doesn't agree with my actual come up.

Graham

Eric32 · Jul 29, 2024

well that was my best guess, or you can try to reduced your velocity to the actual DOPE at 600, maybe you got a bad chrono. Change the BC for 1000yard

Taylorbok · Jul 29, 2024

If you have to dial negative .25 moa to be spot on at 200 that tells me your zero is off. About 1.5 Moa. Which is close to making up the difference at all distances.

Partsunavailable · Jul 29, 2024

2467 velocity shooting 147s? That should be close to 2700, but that's not your dope issue.

6.5SH · Jul 29, 2024

GrahamC said:
So I zeroed at 100 yards and then shot another 60+ rounds at target. Example of my results below, I think after about 40 rounds. What potential issues could I have with my 100 yard zero then, so that I have some idea of what to consider and eliminate?

View attachment 8468696

Based on the screenshot your POI is high for what you are calling "zeroed", look at the center of the entire group.
The next very common possibility (or additional error) is your 100 yards really isn't. Unless you used a tape or good laser it is an assumption.

Taylorbok · Jul 29, 2024

Partsunavailable said:
2467 velocity shooting 147s? That should be close to 2700, but that's not your dope issue.

I believe that is Velocity at the target but still seems a bit slow.

Partsunavailable · Jul 29, 2024

You could try to troubleshoot your problem by using gravity ballistics and forget the ballistic calculator. But the most obvious problem you stated was that you have to dial down to go from 100-200 yards. This is the problem you need to address FIRST, no calculation error can cause this.

Also, if I put my environmentals into 4dof, with a 2700 muzzle velocity. For 600 yards, it tells me 13.8 for dope. Thats within an MOA of the 14.5 you said you needed. Shooter error could cover the rest.

Ledzep · Jul 29, 2024

GrahamC said:
4DOF doesn't appear to have a drag factor. It does have an axial form factor but the max range of adjustment still doesn't agree with my actual come up.

Graham

That's usually a great indication that something is input wrong. I'm guessing scope over bore or zero.

How are you measuring scope over bore and are you sure all of the input/output units are correct in the file?

Long Range 338 · Jul 29, 2024

Ledzep said:
That's usually a great indication that something is input wrong. I'm guessing scope over bore or zero.

How are you measuring scope over bore and are you sure all of the input/output units are correct in the file?

What he said... Also it usually helps to take a step back and start from scratch even though you have already built the profile. Hornady has a bunch of videos on YouTube that walk you thru the process, it really is worth watching to understand how the inputs affect the calculations.

Also I would never use the BC calculator of 4DOF if you are using one of their doppler verified bullets. Use the 4DOF calculator and thank me later.

GrahamC · Jul 29, 2024

Eric32 said:
well that was my best guess, or you can try to reduced your velocity to the actual DOPE at 600, maybe you got a bad chrono. Change the BC for 1000yard

Think the chrono is OK. On the RPR with 24 inch barrel it clocks the round at 2650fps. On the AI with 26 inch barrel, 2700fps which is 5 fps more than Hornady quote for the 147gr 6.5CM ELD-M.

GrahamC · Jul 29, 2024

Partsunavailable said:
2467 velocity shooting 147s? That should be close to 2700, but that's not your dope issue.

That's the velocity the electronic target is registering at the target. Average MV with the AI is 2700fps, as you stated

GrahamC · Jul 29, 2024

6.5SH said:
Based on the screenshot your POI is high for what you are calling "zeroed", look at the center of the entire group.
The next very common possibility (or additional error) is your 100 yards really isn't. Unless you used a tape or good laser it is an assumption.

Yes agree that the POI is slightly high but as the group size is 1.34MOA it's not off by 1.5.

This is the NRA Bisley range in the UK (largest range in Europe apparently). I would be surprised if the distances are inaccurate but fair point as I can't rule that out.

GrahamC · Jul 29, 2024

Partsunavailable said:
You could try to troubleshoot your problem by using gravity ballistics and forget the ballistic calculator. But the most obvious problem you stated was that you have to dial down to go from 100-200 yards. This is the problem you need to address FIRST, no calculation error can cause this.

Also, if I put my environmentals into 4dof, with a 2700 muzzle velocity. For 600 yards, it tells me 13.8 for dope. Thats within an MOA of the 14.5 you said you needed. Shooter error could cover the rest.

Thanks for the pointer, will take a look at the app.

Graham

JerkyFreak · Jul 29, 2024

What is the pressure or altitude you input?

GrahamC · Jul 29, 2024

Ledzep said:
That's usually a great indication that something is input wrong. I'm guessing scope over bore or zero.

How are you measuring scope over bore and are you sure all of the input/output units are correct in the file?

Distance from middle of bore to middle of scope.

The zero @ 100 yards was set some time ago, I then went on to shoot for over a year at 600 yards. When I picked up the AI recently I zeroed that at 100 and also shot the RPR at 100 by returning to zero elevation on the scope and was on target.

My zero may well be wrong but the above had me puzzled. Likely I should go check.

Graham

GrahamC · Jul 29, 2024

Long Range 338 said:
What he said... Also it usually helps to take a step back and start from scratch even though you have already built the profile. Hornady has a bunch of videos on YouTube that walk you thru the process, it really is worth watching to understand how the inputs affect the calculations.

Also I would never use the BC calculator of 4DOF if you are using one of their doppler verified bullets. Use the 4DOF calculator and thank me later.

I was using the 4DOF!

Graham

smoothy8500 · Jul 29, 2024

GrahamC said:
I want to shoot at 1000 yards and have no dope for that.

You got the dope for 600. I just use the "Truing Function" at 500 or 600yds and for my rifles it is correct at 1K.........

GrahamC · Jul 29, 2024

JerkyFreak said:
What is the pressure or altitude you input?

I don't have a Kestrel. For altitude I googled the location to find height above sea level. For pressure I had to use the forecast on the day.
Graham

GrahamC · Jul 29, 2024

Thank you everyone for your suggestions so far, it's appreciated. While it may seem like I'm disagreeing with people I'm actually expressing my puzzlement given I thought I had done all these things right.

Seems like I should try three things: check my zero, check the app settings, cross reference across gravity ballistics app.

Graham

6.5SH · Jul 29, 2024

GrahamC said:
I don't have a Kestrel. For altitude I googled the location to find height above sea level. For pressure I had to use the forecast on the day.
Graham

Were you entering the pressure as is from the weather forecast directly?

Taylorbok · Jul 29, 2024

GrahamC said:
Yes agree that the POI is slightly high but as the group size is 1.34MOA it's not off by 1.5.

The only things I can think of that would cause a need to dial down at 200 are a Zero issue or a huge height over bore.

308pirate · Jul 29, 2024

Taylorbok said:
The only things I can think of that would cause a need to dial down at 200 are a Zero issue or a huge height over bore.

Seems that everyone but you is missing the forest for the trees.

SanPatHogger · Jul 29, 2024

Taylorbok said:
The only things I can think of that would cause a need to dial down at 200 are a Zero issue or a huge height over bore.

I was thinking scope height too. The other times I've had messed up numbers were because my calculator somehow got onto meters per second or meters instead of yards.
Check all your inputs. Bad info in, bad out.

BrassGoblin03 · Jul 30, 2024

Figure out the range the bullet is going transonic and shoot at that range to true your data. For example, with a .308 I would shoot at 800 yards (transonic range) see where my actual impacts are and adjust my muzzle velocity accordingly until the ballistic cal. matches the actual impacts. It will true your data at all ranges without having to shoot every 100 yards. No need to chrono, and also using a set drag model and not a custom one is only a guess. Todd Hodnett goes into extreme depth on this, very easy concept and saves ALOT of ammo. ENSURE your enviromentals are accounted for.

GrahamC · Jul 30, 2024

BrassGoblin03 said:
Figure out the range the bullet is going transonic and shoot at that range to true your data. For example, with a .308 I would shoot at 800 yards (transonic range) see where my actual impacts are and adjust my muzzle velocity accordingly until the ballistic cal. matches the actual impacts. It will true your data at all ranges without having to shoot every 100 yards. No need to chrono, and also using a set drag model and not a custom one is only a guess. Todd Hodnett goes into extreme depth on this, very easy concept and saves ALOT of ammo. ENSURE your enviromentals are accounted for.

Interesting approach and hadn’t heard of this before.

How do I figure out the transonic distance though? If it’s past 1200 yards I don’t have a range long enough!

Taylorbok · Jul 30, 2024

GrahamC said:
Interesting approach and hadn’t heard of this before.

How do I figure out the transonic distance though? If it’s past 1200 yards I don’t have a range long enough!

Your ballistic program will tell you where it goes trans. If you watch those Hodnet videos IIRC you should actually true at mach 1.2 ish.

None of this matters though, you need to figure out the actual issue to why are you having to dial down at 200?
(unless you have like a 6" HOB)

BrassGoblin03 · Jul 30, 2024

Taylorbok said:
Your ballistic program will tell you where it goes trans. If you watch those Hodnet videos IIRC you should actually true at mach 1.2 ish.

None of this matters though, you need to figure out the actual issue to why are you having to dial down at 200?
(unless you have like a 6" HOB)

I agree with this 100%. Without a solid base everything else is a fruitless exercise.

Ronws · Jul 30, 2024

6.5SH said:
Based on the screenshot your POI is high for what you are calling "zeroed", look at the center of the entire group.
The next very common possibility (or additional error) is your 100 yards really isn't. Unless you used a tape or good laser it is an assumption.

This, right here. I go to any range and take my laser and guarantee it will be more like 99.5 yard or close to 99. Input zero distance at what you are actually measuring.

Also, a long time ago, in the before times, there was a famous sniper who would DOPE his rifle the old fashion way. Shoot at each distance and walk out and find the corrections needed and go back and shoot what is now a cold rifle and do it again.

"Shooting a rifle precisely is not hard. Just tedious."

Point being, use actual data from the field to fine tune the app parameters.

DocRDS · Jul 31, 2024

NO NO NO NO

First of all you need to "true" your ballistics program. MV and BC and tunable parameters. You don't just read them off the box and expect them to work. That gets you close, but you need to adust them (or the Hornady "form factor"--I forget what its called) to your real life dope.

However a HUGE red flag is having to dial down at 200. That means either your zero is off or you suck at shooting. Sir, we obey the laws of physics and unless you got some weird ass rounds your bullet is gonna drop at 200--even if it is small.

Looking at your picture your zero is actually "high"

I can "transfer" dope between my 6.5 (same round) by adjusting MV and keeping the BC/FF the same. Both of them have a slight drop at 200. If you have to dial down for 200 after zeroing at 100, you aren't zero'd at 100. Plain and simple.

Dot3 · Aug 1, 2024

GrahamC said:
Yes agree that the POI is slightly high but as the group size is 1.34MOA it's not off by 1.5.

This is the NRA Bisley range in the UK (largest range in Europe apparently). I would be surprised if the distances are inaccurate but fair point as I can't rule that out.

I may have missed something but, you’ve been talking in yards and looks like the range is in the UK, so I’m going out on a limb saying that maybe the range is in meters.

JerkyFreak · Aug 1, 2024

The UK ranges are still in yards.

Ledzep · Aug 1, 2024

DocRDS said:
NO NO NO NO

First of all you need to "true" your ballistics program. MV and BC and tunable parameters. You don't just read them off the box and expect them to work. That gets you close, but you need to adust them (or the Hornady "form factor"--I forget what its called) to your real life dope.

....

With modern radar chronographs, if you need to tune MV in the solver to get things to line up, it's an indication of an incapability of the solver to correctly handle drag data. The MV is what the MV is. If it's not changing and you have to change it in the solver, the solver isn't handling the drag correctly. For 3DoF point mass solvers and especially back in the days of optical chronographs, fair enough-- I think it's well established that that comes with the territory. However, my experience is that with 4DoF (and maybe with some of the other solvers that are doppler drag based, I don't use them and don't know), you want to keep MV as true to real life as possible. For starters, shifting MV shifts the Mach regime around and pulls the wrong Cd data from the Cd vs. Mach curves.

Sight over bore at the objective lens, twist rate, MV, and zero range (or zero angle in 4DoF) need to be nutted. If they are, you should have no problem inside of 600-800yd, and the only problems that show up past 600-800yd are those that can be quickly fixed with axial form factor or adjusting BC. If at that point you still have deviations, it points to optic tracking, POI wander, etc. If you're diligent, the calculating/data measurement tools today are getting to the point that you shouldn't have issues like this.

Agreed on the point of having to dial "down" for 200yd. Optics/zero or inputs are incorrect or not tracking somewhere.

GrahamC · Aug 1, 2024

DocRDS said:
NO NO NO NO

First of all you need to "true" your ballistics program. MV and BC and tunable parameters. You don't just read them off the box and expect them to work. That gets you close, but you need to adust them (or the Hornady "form factor"--I forget what its called) to your real life dope.

However a HUGE red flag is having to dial down at 200. That means either your zero is off or you suck at shooting. Sir, we obey the laws of physics and unless you got some weird ass rounds your bullet is gonna drop at 200--even if it is small.

Looking at your picture your zero is actually "high"

I can "transfer" dope between my 6.5 (same round) by adjusting MV and keeping the BC/FF the same. Both of them have a slight drop at 200. If you have to dial down for 200 after zeroing at 100, you aren't zero'd at 100. Plain and simple.

Have started reading Applied Ballistics for Long Range Shooting by Bryan Litz and it's interesting to read that BC varies over distance due to velocity changes. So I suspect the quoted BC by Hornady is at MV, so you are right.

Regarding my 100 yard 10 round group, the inner ring on the actual target is 1 inch diameter. To adjust the overall grouping to be perfectly centered needs a drop in elevation of 0.20MOA. I may well suck at shooting but probably not ridiculously so

Dropping by 0.25MOA would change my 200 yard elevation from -0.25MOA to 0MOA. Given the difference in time of flight is 0.118s would the gravitational effect actually make a significant difference between 100 and 200 yards?

GrahamC · Aug 1, 2024

JerkyFreak said:
The UK ranges are still in yards.

Correct.

GrahamC · Aug 1, 2024

Ledzep said:
With modern radar chronographs, if you need to tune MV in the solver to get things to line up, it's an indication of an incapability of the solver to correctly handle drag data. The MV is what the MV is. If it's not changing and you have to change it in the solver, the solver isn't handling the drag correctly. For 3DoF point mass solvers and especially back in the days of optical chronographs, fair enough-- I think it's well established that that comes with the territory. However, my experience is that with 4DoF (and maybe with some of the other solvers that are doppler drag based, I don't use them and don't know), you want to keep MV as true to real life as possible. For starters, shifting MV shifts the Mach regime around and pulls the wrong Cd data from the Cd vs. Mach curves.

Sight over bore at the objective lens, twist rate, MV, and zero range (or zero angle in 4DoF) need to be nutted. If they are, you should have no problem inside of 600-800yd, and the only problems that show up past 600-800yd are those that can be quickly fixed with axial form factor or adjusting BC. If at that point you still have deviations, it points to optic tracking, POI wander, etc. If you're diligent, the calculating/data measurement tools today are getting to the point that you shouldn't have issues like this.

Agreed on the point of having to dial "down" for 200yd. Optics/zero or inputs are incorrect or not tracking somewhere.

Twist rate is easy (1:8 on both rifles according to manufacturer specs), MV via a doppler chronograph. I re-checked sight over bore using digital calipers and it's 2.5 inches not 2.85 as I had originally though. Plugging this data into the Hornday 4DOF shows a 12.45MOA come up which is 2MOA off range reality.

DocRDS · Aug 1, 2024

GrahamC said:
Have started reading Applied Ballistics for Long Range Shooting by Bryan Litz and it's interesting to read that BC varies over distance due to velocity changes. So I suspect the quoted BC by Hornady is at MV, so you are right.

Regarding my 100 yard 10 round group, the inner ring on the actual target is 1 inch diameter. To adjust the overall grouping to be perfectly centered needs a drop in elevation of 0.20MOA. I may well suck at shooting but probably not ridiculously so

Dropping by 0.25MOA would change my 200 yard elevation from -0.25MOA to 0MOA. Given the difference in time of flight is 0.118s would the gravitational effect actually make a significant difference between 100 and 200 yards?

No offense, you aren't there yet. The variations in BC are minute compared to getting your dope right.

Your "drop" at 200 yards should be approximately 0.5 mils or 1.8 MOA assuming your 100 yard zero is correct. Part of shooting is consistensy and it is entirely possible that yuo are seeing inconsistent positioning with your rifle as you move to different distances. That is FAR more likely than seeing variations in BC.

Master the basics first.

Can you keep 1 MOA shot to shot at 100. (No? Practice/Class)
Can you keep 1MOA shot to shot at 200....
300
500
etc...

The farther out you go the more "stuff" you have to contend with. (Wind, BC/Variation, Terrain) If your dope is not roughly 0.5/1.8 (it will vary based on your MV, sight height) at 200 after a 100 yard zero, its YOU. There is almost 0 other "stuff" at 200.

Put away your app for now.
Zero at 100.
Dial 0.5Mils or 1.8 MOA
Shoot at 200. Adjust. if you are more than 3 clicks either way off vertically something is WRONG.

Once you get that sorted get the worksheet here:

Advanced Marksmanship - My "Weaponized Math" now called "GRAVITY BALLISTICS". NEW Worksheet Attached.

SIMPLE * Could not be more effective or efficient Move from 200 yards to 1000 yards with less than a box of ammo. * Needs NO INPUTS - Just your DATA at 200 yards to get started. Mil or MOA. * Doesn't care what your M/V is... * Doesn't care what your bullet weighs or what your BC is... *...

www.snipershide.com

Run through the worksheet. (aka shoot dope to 1k)

Then get your ballistic app out and adjust the MV and BC until it predicts what you measured it the worksheet. It may not be perfect, some high, some low, but get em as close as possible.

Now you trust your ballistics app with VERIFIED data.

Ballistics App=Model. Models need to be tuned.

Almost all modern rifles run approximately 2750 fps, for a 100 yard zero that 0.5 mils/1.8 MOA drop at 200 (there is basically zero BC effect at 200 yards, normally to adjust your BC you look at 800+ dope--depends on person, rough guide, but 200 is all MV). That's the point of gravity ballistics. As you go farther and farther out, your data will get adjusted, but its a general trend of gravity. So if you have to dial DOWN (aka shooting high at 200) something is VERY VERY wrong if you have a 100 yard zero.

st1650 · Aug 1, 2024

DocRDS said:
No offense, you aren't there yet. The variations in BC are minute compared to getting your dope right.

Your "drop" at 200 yards should be approximately 0.5 mils or 1.8 MOA assuming your 100 yard zero is correct. Part of shooting is consistensy and it is entirely possible that yuo are seeing inconsistent positioning with your rifle as you move to different distances. That is FAR more likely than seeing variations in BC.

Master the basics first.

Can you keep 1 MOA shot to shot at 100. (No? Practice/Class)
Can you keep 1MOA shot to shot at 200....
300
500
etc...

The farther out you go the more "stuff" you have to contend with. (Wind, BC/Variation, Terrain) If your dope is not roughly 0.5/1.8 (it will vary based on your MV, sight height) at 200 after a 100 yard zero, its YOU. There is almost 0 other "stuff" at 200.

Put away your app for now.
Zero at 100.
Dial 0.5Mils or 1.8 MOA
Shoot at 200. Adjust. if you are more than 3 clicks either way off vertically something is WRONG.

Once you get that sorted get the worksheet here:

Advanced Marksmanship - My "Weaponized Math" now called "GRAVITY BALLISTICS". NEW Worksheet Attached.

SIMPLE * Could not be more effective or efficient Move from 200 yards to 1000 yards with less than a box of ammo. * Needs NO INPUTS - Just your DATA at 200 yards to get started. Mil or MOA. * Doesn't care what your M/V is... * Doesn't care what your bullet weighs or what your BC is... *...

www.snipershide.com

Run through the worksheet. (aka shoot dope to 1k)

Then get your ballistic app out and adjust the MV and BC until it predicts what you measured it the worksheet. It may not be perfect, some high, some low, but get em as close as possible.

Now you trust your ballistics app with VERIFIED data.

Ballistics App=Model. Models need to be tuned.

Almost all modern rifles run approximately 2750 fps, for a 100 yard zero that 0.5 mils/1.8 MOA drop at 200 (there is basically zero BC effect at 200 yards, normally to adjust your BC you look at 800+ dope--depends on person, rough guide, but 200 is all MV). That's the point of gravity ballistics. As you go farther and farther out, your data will get adjusted, but it’s a general trend of gravity. So if you have to dial DOWN (aka shooting high at 200) something is VERY VERY wrong if you have a 100 yard zero.

High iq post right there.
One or many of your basic inputs are fucked up if you have to come down from 100 to 200.
Has nothing to do with having to true the BC or drag factor or any of that shit. Neither does environmentals.
A crazy sight height input possibly would (maybe you wanted to put 1.5in and entered 15in) but yeah forget about ballistic apps, set up a target at 100,200 and 300 and if you properly zero at 100y and still have to go down to 200 then you have other shit to resolve with your equipment than go play around with ballistic softwares

Ledzep · Aug 1, 2024

GrahamC said:
Twist rate is easy (1:8 on both rifles according to manufacturer specs), MV via a doppler chronograph. I re-checked sight over bore using digital calipers and it's 2.5 inches not 2.85 as I had originally though. Plugging this data into the Hornday 4DOF shows a 12.45MOA come up which is 2MOA off range reality.

It might be worth your time to do a tall tracking test of the optic.

Ronws · Aug 1, 2024

Ledzep said:
It might be worth your time to do a tall tracking test of the optic.

And check torque on everything.

Action screws, rail or base screws. Ring base screws. Ring screws.

Anything else loose?

Got to get your cheek on the comb. If it is too low and you have a non-adjustable stock, do it the old fashioned way and get some craft foam and vet tape and build up a riser that lines your eye up.

If you are not touching the comb with your cheek and you are hovering, your parallax will be off.

Slides · Aug 1, 2024

Are you entering temp data? I'd imagine Bisley is usually lower than standard conditions and would result in more drop than calculated for standard conditions. How you address the rifle/cheek weight can easily shift vertical 1.5MOA too if not consistent.

I usually shoot to 900 yards on electronic targets and even without correcting for atmospherics on the day I'm usually at worst within a few clicks off vertical using 4DOF generated tables with correct chronograph velocity data.

Ichi · Aug 1, 2024

GrahamC said:
Hi all,

I have two rifles chambered in 6.5 Creedmoor (Ruger RPR and Accuracy International AT-X) both with Vortex Razor HD Gen 2 scopes. I shoot at a range with known distances from 100-1200 yards in 100 yard increments.

My rifles are zeroed for 100 yards and I have dope settings for 100, 200, 300 and 600 yards. I've tried a variety of different calculators (Hornady 4DOF, Vortex, several others). They all seem consistent in their come up values which don't match either of my rifles. For instance with the RPR at 600 yards they state around 12.8MOA come up while I have to actually dial 14.5 - a big difference! With the AI, the calculators state 1.35 come up at 200 yards when I actually have to dial -0.25 from my 100 yard zero.

I'm using a Garmin chrono so have accurate MV. I'm using Hornady ELDM 147gr factory ammo so know the bullet weight, am specifying barrel twist, sight height over barrel, temperature etc.

Is there an explanation why the calculators seem so far off vs my two rifles?

I want to shoot at 1000 yards and have no dope for that. How can I use a calculator to determine that? Should I change the bullet G7 BC to accurately match the come up at 600 yards and then use the 1000 yard figure the calculator then suggests?

All gems of experience welcome!

Thanks.
Graham

When using the Hornady 4DOF app, I've found that if you don't go thru the process of setting your "zero angle", the solution will be off.

This is a good video on how to set the zero angle. You need to follow the instructions and be as accurate in your measurements as possible.

GrahamC · Aug 2, 2024

GrahamC said:
Have started reading Applied Ballistics for Long Range Shooting by Bryan Litz and it's interesting to read that BC varies over distance due to velocity changes. So I suspect the quoted BC by Hornady is at MV, so you are right.

Regarding my 100 yard 10 round group, the inner ring on the actual target is 1 inch diameter. To adjust the overall grouping to be perfectly centered needs a drop in elevation of 0.20MOA. I may well suck at shooting but probably not ridiculously so

Dropping by 0.25MOA would change my 200 yard elevation from -0.25MOA to 0MOA. Given the difference in time of flight is 0.118s would the gravitational effect actually make a significant difference between 100 and 200 yards?

1G acceleration is 32 feet per second per second. So 0.118s should equal a 3.7ft drop (assuming linear acceleration and that terminal velocity hasn't been reached).

DocRDS said:
No offense, you aren't there yet. The variations in BC are minute compared to getting your dope right.

Your "drop" at 200 yards should be approximately 0.5 mils or 1.8 MOA assuming your 100 yard zero is correct. Part of shooting is consistensy and it is entirely possible that yuo are seeing inconsistent positioning with your rifle as you move to different distances. That is FAR more likely than seeing variations in BC.

Master the basics first.

Can you keep 1 MOA shot to shot at 100. (No? Practice/Class)
Can you keep 1MOA shot to shot at 200....
300
500
etc...

The farther out you go the more "stuff" you have to contend with. (Wind, BC/Variation, Terrain) If your dope is not roughly 0.5/1.8 (it will vary based on your MV, sight height) at 200 after a 100 yard zero, its YOU. There is almost 0 other "stuff" at 200.

Put away your app for now.
Zero at 100.
Dial 0.5Mils or 1.8 MOA
Shoot at 200. Adjust. if you are more than 3 clicks either way off vertically something is WRONG.

Once you get that sorted get the worksheet here:

Advanced Marksmanship - My "Weaponized Math" now called "GRAVITY BALLISTICS". NEW Worksheet Attached.

SIMPLE * Could not be more effective or efficient Move from 200 yards to 1000 yards with less than a box of ammo. * Needs NO INPUTS - Just your DATA at 200 yards to get started. Mil or MOA. * Doesn't care what your M/V is... * Doesn't care what your bullet weighs or what your BC is... *...

www.snipershide.com

Run through the worksheet. (aka shoot dope to 1k)

Then get your ballistic app out and adjust the MV and BC until it predicts what you measured it the worksheet. It may not be perfect, some high, some low, but get em as close as possible.

Now you trust your ballistics app with VERIFIED data.

Ballistics App=Model. Models need to be tuned.

Almost all modern rifles run approximately 2750 fps, for a 100 yard zero that 0.5 mils/1.8 MOA drop at 200 (there is basically zero BC effect at 200 yards, normally to adjust your BC you look at 800+ dope--depends on person, rough guide, but 200 is all MV). That's the point of gravity ballistics. As you go farther and farther out, your data will get adjusted, but its a general trend of gravity. So if you have to dial DOWN (aka shooting high at 200) something is VERY VERY wrong if you have a 100 yard zero.

OK, thanks for the advice, appreciated

GrahamC · Aug 2, 2024

Ronws said:
And check torque on everything.

Action screws, rail or base screws. Ring base screws. Ring screws.

Anything else loose?

Got to get your cheek on the comb. If it is too low and you have a non-adjustable stock, do it the old fashioned way and get some craft foam and vet tape and build up a riser that lines your eye up.

If you are not touching the comb with your cheek and you are hovering, your parallax will be off.

Yes, I've been re-checking torque and applying Vibra-tite to the screws. Stock and comb are adjustable and my cheek is definitely on it. Parallax setting is correctly set for the actual distance.

GrahamC · Aug 2, 2024

Ichi said:
When using the Hornady 4DOF app, I've found that if you don't go thru the process of setting your "zero angle", the solution will be off.

This is a good video on how to set the zero angle. You need to follow the instructions and be as accurate in your measurements as possible.

Interesting video, thanks.

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