BC Calculator help

[bfk4lyfe]

I'm trying to get some data for my rifle but I'm getting some different results when I use Hornady 4DOF and my Kestrel 5700 ballistics model (non elite). At 200 and 300 they're the same click value but by 400 they start to deviate. I'm using Hornady Black factory ammo @ 2477 FPS (chrono'd today from a MS3), 88 degrees, 471 ft elevation, 18" LaRue 1:8 twist barrel and 2.63" scope height over bore. I'm using a G7 BC of .247, and that's off of Hornady's site to account for the slower moving bullet. I have the same wind conditions entered for both.

4DOF gives me:

200: 1.92 MOA
300: 5.05 MOA
400: 8.84 MOA
500: 13.25 MOA
600: 18.12 MOA

Kestrel gives me:

200: 1.86 MOA
300: 4.87 MOA
400: 8.47 MOA
500: 12.58 MOA
600: 17.23 MOA

Does anyone have any dope for similar conditions that I could compare to? FWIW, when I use Hornady's regular BC calc (aka non 4DOF version), I get the same data as the Kestrel.

[grayfox]

I tried your MV and scope ht values but with the corresponding mach 2.0 G1 of 0.493 in my Strelok and came pretty close to the Kestrel. (I didn't change my Env's - 328 el and 72*).
200 -- 1.85
300 -- 4.85
400 -- 8.41
500 -- 12.46
600 -- 17.01

My guess is that the Hdy 4dof calculator switches to lower BC's as the bullet slows down, so switches to the 1.75 mach value for the 500 and 600... just a guess, though.

[Klem]

Be interesting to see what the actual come-ups are when you are at the range.

Looks like the difference between the two programs is almost moot. You probably have a scope with 1/4" MOA graduations so will be dialling the same come-ups to 500 regardless.

[bfk4lyfe]

My guess is that the Hdy 4dof calculator switches to lower BC's as the bullet slows down, so switches to the 1.75 mach value for the 500 and 600... just a guess, though.

Could be. I tried it with the lowest BC Hornady lists for it but it didn't change it a whole lot though.

Klem,

I'm also curious what the real data is, just wanted to see if anyone had real experience to compare the computer numbers to. OR if anyone had any real life experience in the differences between 4DOF and the various BC versions. I'm stuck at 100 yards except for very special occasions so wanted to be prepared as much as possible.

[Sinclair]

[QUOTE=bfk4lyfe;201490____ I'm stuck at 100 yards except for very special occasions so wanted to be prepared as much as possible.[/QUOTE]

I am in the same boat so I too am very interested in what others get in the real world. Even if two calculators use the same algorithms, if one rounds each operation and the other keeps 20+ decimal places until the final result the two answers could be considerably different. Frankly, I have not found any that consistently give real world results. Pick one that is close for your cartridge/bullet combo and be prepared to interpolate the results. Not being able to shoot out past 300 or 400 yards really puts the damper on getting good data for come ups and wind drift.

[Klem]

I will add that you are looking at a computer output discrepancy of two decimal places. These programs will get you on target but the level of precision you are concerned about is unrealistic. The algorithms that drive these programs are by default, simplifications of reality. There are other factors not being considered. Like the swirling air pushing that bullet around differently to what the flags are showing. Or the difference in temperature of the ammunition and how that changes velocity between when you chronographed it and when you shoot. Little things like how long has that auto-loaded round been sitting in the hot chamber (oven) before you pull the trigger. Or what exactly your scope reticle has moved regardless of what the turret clicks say. Or how much the erector mechanism has moved from the last recoil as you chase the spotter around on the target.

Applied Ballistics sells custom drag models for their program they claim make the computed curve more precise. This is especially relevant at Mach 1.5 and below as G1 and G7 curves diverge.

I can't remember the last time a ballistics calculation put a bullet exactly where it said it should go to my definition of accuracy. But, they get you on steel/paper and that means a 'hit' on what you are shooting at.

[LRRPF52]

I'm trying to get some data for my rifle but I'm getting some different results when I use Hornady 4DOF and my Kestrel 5700 ballistics model (non elite). At 200 and 300 they're the same click value but by 400 they start to deviate. I'm using Hornady Black factory ammo @ 2477 FPS (chrono'd today from a MS3), 88 degrees, 471 ft elevation, 18" LaRue 1:8 twist barrel and 2.63" scope height over bore. I'm using a G7 BC of .247, and that's off of Hornady's site to account for the slower moving bullet. I have the same wind conditions entered for both.

4DOF gives me:

200: 1.92 MOA
300: 5.05 MOA
400: 8.84 MOA
500: 13.25 MOA
600: 18.12 MOA

Kestrel gives me:

200: 1.86 MOA
300: 4.87 MOA
400: 8.47 MOA
500: 12.58 MOA
600: 17.23 MOA

Does anyone have any dope for similar conditions that I could compare to? FWIW, when I use Hornady's regular BC calc (aka non 4DOF version), I get the same data as the Kestrel.

Convert all your drop and drift data into a practical, usable format. Is it clickable or can you hold to that decimal?

200: 1.92 MOA = 2 MOA
300: 5.05 MOA = 5 MOA
400: 8.84 MOA = 8.75 MOA if you have 1/4 clicks, 9 MOA for half MOA clicks
500: 13.25 MOA = 13.25 MOA for 1/4 clicks, 13 MOA for half
600: 18.12 MOA = 18 MOA

Kestrel gives me:

200: 1.86 MOA = 1.75 or 2 MOA
300: 4.87 MOA = 4.75 or 5 MOA
400: 8.47 MOA = 8.5 MOA
500: 12.58 MOA = 12.5 MOA
600: 17.23 MOA = 17.25 or 17 MOA

What's .75 MOA difference at 600yds? 4"

If you have an MOA reticle for holds, you're looking at 2 MOA hashes on most of them.

[Klem]

For ease of range cards you could use a rounding formula in Excel. The one used here is MROUND. It rounds up or down to the nearest multiple. If you're dealing with MOA tactical scopes they are typically either 1/4 or 1/2MOA clicks. In decimal-speak that's multiples of 0.25 or 0.5.

Fill a column with what the ballistics program is predicting. Then fill the next column with what your scope clicks are (1/4 or 1/2). Then in the next column type =MROUND(a,b)

a is the cell with the ballistics prediction and,
b is the cell with the click graduations. Fill down to populate all the predictions.