Box velocity vs chrono vs trued to distance velocity

Thank you I’ll play with bc. Excuse my ignorance, new to 500+ shooting and def new to having a chrono



That Hornady podcast beginning around minute 50 discusses with graphs and charts what is going on with a bc vs actual drag of the bullet and what happens when you start truing. I’m not qualified to give advice as to what matters and when and what you should do, but I find this stuff interesting.

For my part, for my first NRL Hunter match I chronoed my load using my Garmin and used the Litz G7 bc for my bullet loaded into my solver. I tested it at 547 yards before I went and it was fine. I was getting hits out to 850ish at the match and never felt like my trajectory prediction was the cause of any miss. Maybe I was lucky, or maybe I suck too much to be able to tell. YMMV.
 

That Hornady podcast beginning around minute 50 discusses with graphs and charts what is going on with a bc vs actual drag of the bullet and what happens when you start truing. I’m not qualified to give advice as to what matters and when and what you should do, but I find this stuff interesting.

For my part, for my first NRL Hunter match I chronoed my load using my Garmin and used the Litz G7 bc for my bullet loaded into my solver. I tested it at 547 yards before I went and it was fine. I was getting hits out to 850ish at the match and never felt like my trajectory prediction was the cause of any miss. Maybe I was lucky, or maybe I suck too much to be able to tell. YMMV.
I’ll have to give that a listen. I definitely feel like I’ve lucked into my solution..
 
@Formidilosus

I have a bit of a run on question. If your scope is verified to track, your zero is confirmed, environmentals are input correctly, height over bore is correct, velocity is known and BC used in your calculator is off a box of bullets yet your actual drops don’t match the calculations what would you recommend to be the metric that needs to be changed to allow your calculator to provide an accurate flight profile that can be modified to changing environments and temp adjusted velocities?

The BC on the box may or may not be correct. Berger, Sierra, and Hornady ELD-M/X’s have correct real BC’s. Others generally not. If you are using unverified numbers, especially solid coppers- yes, the BC is probably not correct.

As for everything being measured and correct and the data not lining up- in hundreds upon hundreds of rifles, I have not seen one not track within .1 mil of the data provided- if all the data is correct. BC variation from rifle to rifle is ridiculously low- so low that it becomes a joke for the vast majority of shooters to be touching it. Put plainly, if one is using a verified G1 or G7 BC, and their data is off- it isn’t because of the BC.



As far as I’m aware, it’s only the BC/drag profile that can be corrected that will provide good data as environmentals (including temperature adjusted velocity) change. If there is another metric that fine tunes my dope more accurately I’d like to know.


The issue is that one cannot see the tiny difference in BC from rifle to rifle of actual measured BC from a bullet.

6mm 108gr ELD-M, 2,940fps MV.

Real .536 G1 bc.
IMG_5544.jpeg


10 points lower- about the maximum you will see in variation-
IMG_5545.jpeg


A whopping .1 mil difference at 1,200 yards. They are exactly the same to 950 yards.

The amount of people who could actually see and positively determine that a .1 mil difference at 1,200 yards is from the BC variation- and not from the dozens of other variables is laughably low. Positively perfect zero with high shot group- 20+ round group perfectly centered and/or offset input. Track reticle movement and precision at least every 1 mil for 10+ mils- and at least a 10 shot group at every mil…. It must be live fire, as lots of scopes get erector jump from recoil that doesn’t show on a static tracking board. Do this multiple times to get an average; input the average correctly.
Conditions perfectly measured- temp, BP, altitude, etc. Somehow get an area with absolutely zero wind the entire flight path of 1,200 yards. Then, shoot that same 20+ shot group on a single target, and measure the offset from center perfectly.


Again, it is near functionally impossible for people to positively determine if slight variations in BC are causing a .1 mil difference- at the ranges where a BC variation is causing a .1 mil difference. At sub 1,200’ish yards with most combinations that shooters are using, using a real BC is certainly not causing .3-.4 mils differences. Not even close.
 
RF binos have to acclimate to ambient temp- pulled straight out of a heated or air conditioned vehicle, or letting the sun, or kept in a bino harness on a cold day- they will read off.

Could you elaborate on this a bit - what kind of "off" are we talking? As in, short or long, how much at a given distance, etc. I'm considering picking up a pair of the Leica Geovids with the AB app, if it matters.
 
Could you elaborate on this a bit - what kind of "off" are we talking? As in, short or long, how much at a given distance, etc. I'm considering picking up a pair of the Leica Geovids with the AB app, if it matters.

If it’s really cold outside (single digits) and the binos are against your chest- especially if under a jacket say, the difference in data given can be quite a bit- .4 to .5 mils at 800’ish yards is what I have seen.

It’s easy to deal with- just let them reach ambient- keep them out of jackets, open the lid of the bino harness if it’s not snowing or raining, keep them shaded if it’s hot, etc.
 
If it’s really cold outside (single digits) and the binos are against your chest- especially if under a jacket say, the difference in data given can be quite a bit- .4 to .5 mils at 800’ish yards is what I have seen.

It’s easy to deal with- just let them reach ambient- keep them out of jackets, open the lid of the bino harness if it’s not snowing or raining, keep them shaded if it’s hot, etc.

That's great info, thank you.
 
Appreciate all the info!
The BC on the box may or may not be correct. Berger, Sierra, and Hornady ELD-M/X’s have correct real BC’s. Others generally not. If you are using unverified numbers, especially solid coppers- yes, the BC is probably not correct.
regarding the accuracy of the BC on the box of ELDM’s, in AB when I select it from their bullet library it auto populates a G1 of .589 compared to the .646 that is on the box. I just type in the box bc and move on but is this something that AB tested and got a different bc compared to hornady’s 4dof?

As far as the rest, I’ll be doing a tall target test to get my scope tracking figured out.
 
Appreciate all the info!

regarding the accuracy of the BC on the box of ELDM’s, in AB when I select it from their bullet library it auto populates a G1 of .589 compared to the .646 that is on the box. I just type in the box bc and move on but is this something that AB tested and got a different bc compared to hornady’s 4dof?

That’s a thing in itself. The G1 Mach 2.25 BC given by Hornady results in good data to at least around 1,600fps impact. If you use AB’s numbers- impacts are pretty consistently high.
Of course, in 4 DOF, there are some weird outputs for non Hornady bullets- especially Bergers. Yet using Bergers stated BC’s, you get pretty consistent data matching.

Hornady, Berger, and Sierra all produce good BC numbers now days. Good results are had when using each companies stated numbers.
 
Ive noticed this too, AB modified BC’s are extremely low for shooting to 1k, at least with a variety of bergers and sierras. They seem to be closer than the box on other brands. I am fairly new to AB, since Strelok became no longer supported. When transferring my data over I played around with AB’s data and found I’d be sailing high compared to my verified data.
 
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