Need help understanding why my ballistics calculator is doing this!!

[CRNA]

Ok, to be brief I will try and get down to brass tacks.

I shoot a 7RM. Chronoed the load of Bergers to be avg. of 2900 FPS. These are 168gr. Bergers.

I use ballistic FTE on my ipod touch. Went shooting yesterday at 1060yds and 1120yds.
My calculator gave me the dope: 25MOA elevation. I shot. Boiled the dust about 6 feet above the target!!! Corrected the dope and ended up hitting the target consistently with 21 MOA. How could that be.

Went on to shoot 1120. Same thing. Calculator called for 29MOA. Hit way high. Rang the target once I dialed back to 24MOA.

So I get back and played with the numbers. I thought that there may have been a misreading of the chrono, but turns out, I would have to be shooting a bullet 200FPS faster than I chronoed to make the drops work. No way I'm loading this round to 3100FPS.

Then I play with the BC numbers. My calculator recalls from it's library of bullets that the Berger 168gr VLD has a G1 BC of .617. When I select G1 for my ballistic profile I get the drops mentioned above. When I tell the calculator to use the G7 BC profile my numbers are almost dead-nuts on. Now at this point I thought "problem solved", but the drop chart generated by the calculator shows the BC of the bullet (.617) but with a G7 profile. (G7 for the 168gr Berger VLD is actually .316 I believe). I was under the assumption that if I used the G1 profile for my bullet in the calculator I would designate it to use the G1 BC. What gives. It's like I'm using the G1 BC number, but telling the calculator to use a G7 profile. ?????? I thought if I were using the G7 profile, then I would have to use the BC of .316?

I hope this isn't confusing as hell to you guys. But it really has stumped me. I believe anybody with any rifle can throw enough rounds down range to finally hit the target, but in my opinion, if you can't make first shot hits then the whole setup is useless. I missed both targets by FEET, not inches.

Any insight before I have a stroke over here?

 

[Mikecr]

if you can't make first shot hits then the whole setup is useless

And so is shooting at ~1100yds if you can't shoot at ~500yds..
So how accurate are you shooting with this system at 500?

 

[dig]

Silly question but are your adjustment for sure in MOA or may the be in IPHY? Have made that mistake before and your really dont notice it until you get out there beyond about 700.

 

[Bart B]

Silly question but are your adjustment for sure in MOA or may the be in IPHY? Have made that mistake before and your really dont notice it until you get out there beyond about 700.

In the shooting sports here in the USA, they're both the same. That came to be long ago when both smallbore and highpower target rings were spaced in even inches apart.

That was established over a hundred years ago when externally adjusted scopes' rear mounts moved .0002" per 1/4th moa click and their 7.2 inch base spacing moved the scope 1/4 inch per hundred yards. Such is life when their adjustment screws have 40 threads per inch and the detent ring makes their spring loaded ball cllick 50 times per revolution. .025 inch per thread divided by 50 equals .0002 inch per click.

And metallic aperture sights were made with their adjustment lead screws had 40 threads per inch. One turn of the knob with a standard 30 inch sight radius moved the aperture .025 inch and one third of that's .008333 inch which is 1/3600th of the sight radius so 1/3600th of 100 yards is exactly one inch.

The above aside, some scopes are not quite exactly 4 clicks per inch at 100 yards because the thread pitch and spacing between the erector tube's pivot point and the adjustment flats aren't such to be exactly on. Measure the click value by clampng your scope in a vise then seeing how far the reticule moves for 40 clicks on a target at 100 yards. If it's anything but exactly 10 inches on the target, note what the error is.

Forget the trigonometric value that puts 1 moa of trig equalling about 1.0472 inch.

 

[Loner]

They may have been the same but no so anymore. If you order a mid or high end scope
in iphy or moa it will be much closer than the 4.5% difference in the two. IIRC I use
.23877 in custom settings to get 1/4 iphy instead of 1/4 moa clicks. In any case it's only
2 moa of a 5 moa problem. Maybe your weather data is what bit you. It can get confusing
with zero weather, standard and station pressure, etc.. You'll have to study your settings
and what they mean to figure it out. As far as the bc, you choose that when you enter the
load, I don't think you can change it in heads up. I think you have to choose it in settings
and then shut the program down to get it to take the switch? (do you know how to kill
the programs in the ipod?)

And you didn't say what scope you are running?

 

[Scot E]

There are so many things it could be, gonna take you some time to figure it out.

First, a ballistic engine like FTE is just a estimation tool. at those distances atmospheric conditions, scope height, spin drift, Coriolis affect, and wind values are going to have to be spot on or you will find large variances. Getting proper numbers for pressure and altitude will cause some big variances. I am not familiar with FTE so I don't know options are best.

Also, G7 and G1 BC's will vary to especially at further distances.

Have you checked your scope click values? Often overlooked and can cause huge variances.

The updraft from a cross wind blowing over rises in the landscape can also increase bullet POI by feet!

What is the size of your groups at your zero or some other closer distance?

Even if all of the above is fine you still have to go out and verify your drops. I don't know many LR guys that have their drops line up perfectly with their calculators.

 

[dig]

Interesting, in talking with the Leopold Technical Support Representatives they informed me the older VXIII models where in IPHY and the new models are now in MOA again at 1.047 as stated, when stretching distance it makes a difference. Also, most modern ballistic programs offer a choice in IPHY or MOA. After speaking with Leupold and changing my adjustments to MOA I was spot on with adjustments.

 

[Loner]

Right on Scot, I line FTE up with my verified data not the other way around.

 

[damoncali]

Then I play with the BC numbers. My calculator recalls from it's library of bullets that the Berger 168gr VLD has a G1 BC of .617. When I select G1 for my ballistic profile I get the drops mentioned above. When I tell the calculator to use the G7 BC profile my numbers are almost dead-nuts on. Now at this point I thought "problem solved", but the drop chart generated by the calculator shows the BC of the bullet (.617) but with a G7 profile. (G7 for the 168gr Berger VLD is actually .316 I believe). I was under the assumption that if I used the G1 profile for my bullet in the calculator I would designate it to use the G1 BC. What gives.
Any insight before I have a stroke over here?

You are correct. If you use a G7 drag function you must use a G7 BC. I'm not terribly familiar with that software, but if the results improved (as one might expect when going from G1 to G7), I would guess it might be a software bug that is simply displaying the wrong drag function's BC, while using the correct one.

Now if you're really using the G1 BC with a G7 drag function and getting accurate results, something is quite wrong and you are just getting it right by coincidence.

Another comment: There is only one proper drag function for a bullet. It's either G7 or G1 and this doesn't change. For almost all long range bullets, the best choice is G7. This is why I love Bryan Litz's book - it tells you which one to choose. This is the method I used for my own software - you pull a bullet from the library and the software chooses a BC and drag function for you. It's simpler that way.

Try rerunning it on my software (it's free): Bison Ballistics Calculator

If you get similar numbers, I can tell you for sure what BC and drag function were used. (I'm fairly certain it's a G7 for that bullet, but I don't publish the BC's on the site out of respect of Bryan's work.)

Finally, 1000+ yards is a long way. There are limits to this technology. The further out you go, the more you have to nail the inputs to get a good result.

 

[Bart B]

They may have been the same but no so anymore. If you order a mid or high end scope in iphy or moa it will be much closer than the 4.5% difference in the two.

You're not quite correct.

In competitive bullseye shooting, they still are the same. And there's a 4.72% difference, not a 4.5%

It's the hunting sports where it's sometimes changed. Some folks in that group of shooters never could get the two figured out and separated. Same thing for what was the standard term for focusing a rifle scope on the target so its front objective lens would focus the target image exactly on the reticule. Most folks couldn't understand what focusing for target range meant 'cause their concerns were almost always about parallax. So some scope companies started calling that adjustment the "parallax adjustment" not even commenting that the only way to adjust parallax was to move ones eye from off the scope's optical axis back to right on it. Nor even that when the aiming eye's exactly on the scope's optical axis, there's no parallax regardless of what range the scope's focused at.

I wonder if folks using scopes with ajustments graduated in mils know that there's four world standards on how much of an angle one mil's worth and which one their scope uses.

The above aside, what scope makers offer both standards?

 

[Scot E]

You're not quite correct.

In competitive bullseye shooting, they still are the same. And there's a 4.72% difference, not a 4.5%

It's the hunting sports where it's sometimes changed. Some folks in that group of shooters never could get the two figured out and separated. Same thing for what was the standard term for focusing a rifle scope on the target so its front objective lens would focus the target image exactly on the reticule. Most folks couldn't understand what focusing for target range meant 'cause their concerns were almost always about parallax. So some scope companies started calling that adjustment the "parallax adjustment" not even commenting that the only way to adjust parallax was to move ones eye from off the scope's optical axis back to right on it. Nor even that when the aiming eye's exactly on the scope's optical axis, there's no parallax regardless of what range the scope's focused at.

I wonder if folks using scopes with adjustments graduated in mils know that there's four world standards on how much of an angle one mil's worth and which one their scope uses.

The above aside, what scope makers offer both standards?

Fortunately none of that stuff matters, or at least it shouldn't. If guys will just check and measure their click adjustments and use those numbers in their ballistic programs they will be good to go and find that there numbers are much closer to the ballistic profile than it was.

So many get all caught up in the math. If you are using MOA, IPHY, or MIL correctly then the math shouldn't even come into play. This is especially true in today's world of laser rangefinders.

This is one of the reasons I think more guys need to look at using ballistic reticles. This takes a huge segment of the potential error and removes it completely.

 

[bigngreen]

Ok, to be brief I will try and get down to brass tacks.

I shoot a 7RM. Chronoed the load of Bergers to be avg. of 2900 FPS. These are 168gr. Bergers.

I use ballistic FTE on my ipod touch. Went shooting yesterday at 1060yds and 1120yds.
My calculator gave me the dope: 25MOA elevation. I shot. Boiled the dust about 6 feet above the target!!! Corrected the dope and ended up hitting the target consistently with 21 MOA. How could that be.

Went on to shoot 1120. Same thing. Calculator called for 29MOA. Hit way high. Rang the target once I dialed back to 24MOA.

So I get back and played with the numbers. I thought that there may have been a misreading of the chrono, but turns out, I would have to be shooting a bullet 200FPS faster than I chronoed to make the drops work. No way I'm loading this round to 3100FPS.

Then I play with the BC numbers. My calculator recalls from it's library of bullets that the Berger 168gr VLD has a G1 BC of .617. When I select G1 for my ballistic profile I get the drops mentioned above. When I tell the calculator to use the G7 BC profile my numbers are almost dead-nuts on. Now at this point I thought "problem solved", but the drop chart generated by the calculator shows the BC of the bullet (.617) but with a G7 profile. (G7 for the 168gr Berger VLD is actually .316 I believe). I was under the assumption that if I used the G1 profile for my bullet in the calculator I would designate it to use the G1 BC. What gives. It's like I'm using the G1 BC number, but telling the calculator to use a G7 profile. ?????? I thought if I were using the G7 profile, then I would have to use the BC of .316?

I hope this isn't confusing as hell to you guys. But it really has stumped me. I believe anybody with any rifle can throw enough rounds down range to finally hit the target, but in my opinion, if you can't make first shot hits then the whole setup is useless. I missed both targets by FEET, not inches.

Any insight before I have a stroke over here?

Could you post up you complete data, it looks like FTE has JBM as a ballistics engine so I would use JBM online and help it to get squared away.

Copied from site, some of the answer may be in this. It may convert but not display the new number.

• Automatic Drag Model Conversions
  Automatically convert between two different drag models. Ballistic will recalculate the ballistic coefficient and adjust its trajectory to fit the new drag model. This is ideal if you only have a G1 coefficient for a VLD, spire point, or other type of uniquely-shaped projectile, as it allows you to apply a more accurate drag calculation. This may improve your long range accuracy beyond that of the standard G1 calculation provided by the manufacturer. Wish your manufacturer produced stepped BCs? Convert the drag model to apply a more suitable drag.

 

[Loner]

There are two computers to choose from, JBM and Ballistic. You make the choice in
general settings. And again you have to "kill" the program for the change to take.

 

[Loner]

A millidradian is 1/6,283.2 of a circle. (1/6400 is nato) or .0573 degrees. 3.4377 minutes in a mil. Mils are
based on radians, moa on degrees minutes and seconds. One moa is 1.047 inches at
100, SMOA is one inch @ 100 and a mil is 3.6 @ 100 yards. I don't know how to get
anything but .955 or .9551098 to be precise from converting moa to smoa. That is .04489 or 4.5%. Where is the math wrong. I have to admit I get mixed up sometimes.

USO builds scopes in smoa unless they specify it is true moa. They do build both in normal production. Lupy for years built smoa and has since switched to true moa. Vortex is
true moa. My Swaro (13 years old) is mil on the clicks .36 inches per click. You just have to read the manufacturers specs, they all list them. But then they have to be verified.
Up until recently most were not true to spec. As the shooting world gets into dialing they get better and better.