Do you adjust MV or BC value of a ballistic app when field proven the ballistics?

[Shortschaf]

The Hornady 2.25 Mach Value for a 147 ELDM is .351 and i have ran a .320 out of my last 2 NRL Hunter Rifles, a factory Bergara was .330, and my PRS rifle was a .330. (Those numbers won 3 matches and have 2 more top 3s) That matches up to the provided Mach 2.0 BC but the .351 is whats on the box. I ran the velocity off my Chrono and then trued the BC from there. As far as i know thats how everyone winning in PRS and NRL Hunter does it. I have found that trueing the BC is a more accurate way for all the rifles i have been around.

This kind of stuff is precisely what I mean in my earlier comments about box values being unreliable.

I don't look at box values for anything. The Applied Ballistics library is put together with live fire doppler testing of all common bullets.
Pulling up the 147 ELDM in AB gives a 0.316 G7 BC. Hornady advertises 0.351

The 140 ELDM pulls up with 0.296 in AB. Hornady advertises 0.326

Hornady is a significant offender of inflated BC's if you are a believer of AB data as I am.
I use their library BC's (which almost always have a lower value than box), input speeds from the chrono, and dope lines up excellent

 

[huntnful]

This kind of stuff is precisely what I mean in my earlier comments about box values being unreliable.

I don't look at box values for anything. The Applied Ballistics library is put together with live fire doppler testing of all common bullets.
Pulling up the 147 ELDM in AB gives a 0.316 G7 BC. Hornady advertises 0.351

The 140 ELDM pulls up with 0.296 in AB. Hornady advertises 0.326

Hornady is a significant offender of inflated BC's if you are a believer of AB data as I am.
I use their library BC's (which almost always have a lower value than box), input speeds from the chrono, and dope lines up excellent

I’m not familiar with all of the AB BC’s, but aren’t they derived from longer ranges? I’m not sure the ranges or anything. Just what I’ve heard, so I’d be curious if someone had more in depth knowledge of their BC info.

I true my BC’s at 1200 yards, and they normally come up a little low at that distance when using manufacturer BC’s. But they don’t come up low at 5-600 yards.

 

[Formidilosus]

This kind of stuff is precisely what I mean in my earlier comments about box values being unreliable.

I don't look at box values for anything. The Applied Ballistics library is put together with live fire doppler testing of all common bullets.
Pulling up the 147 ELDM in AB gives a 0.316 G7 BC. Hornady advertises 0.351

The 140 ELDM pulls up with 0.296 in AB. Hornady advertises 0.326

Hornady is a significant offender of inflated BC's if you are a believer of AB data as I am.
I use their library BC's (which almost always have a lower value than box), input speeds from the chrono, and dope lines up excellent

AB undervalues Hornady bullets, especially ELD-M a lot. Or more precisely AB is averaging the BC, or using a lower Mach. However, for the vast majority of hunters and shooters, Mach 2.25 lines up better overall from muzzle to 800 yards plus, or if most ones shooting is beyond 800 yards, Mach 2 value works.
It doesn’t take much googling to find a common trend with people using ELD-M’s and AB is that they are having to screw with BC and data a bunch. Hornady is using Doppler like everyone doing it correctly.

On the flip side, in 4 DOF when not using Hornady bullets, windage outputs will be pretty wild from AJ- with Hornady bullets, it’s as expected.

 

[COPrecisionRifle]

This kind of stuff is precisely what I mean in my earlier comments about box values being unreliable.

I don't look at box values for anything. The Applied Ballistics library is put together with live fire doppler testing of all common bullets.
Pulling up the 147 ELDM in AB gives a 0.316 G7 BC. Hornady advertises 0.351

The 140 ELDM pulls up with 0.296 in AB. Hornady advertises 0.326

Hornady is a significant offender of inflated BC's if you are a believer of AB data as I am.
I use their library BC's (which almost always have a lower value than box), input speeds from the chrono, and dope lines up excellent

Theres so many factors that i wouldnt say they are inflating the numbers. Speed, Twist, barrel grove, bore diameter, grove diameter, grove width etc will all impact how the bullet looks leaving the muzzle. A guy shooting a 6.5-300 weatherby and a guy shooting a 6.5 creed will see different BC numbers out of the same box of bullets. Thats why i true BC though because its the only input that i cannot measure myself. All other inputs are measured from my rifle at that time so unless my chrono or kestrel is giving incorrect data then thats the only factor that can be changed without fudging the numbers.

 

[Shortschaf]

AB undervalues Hornady bullets, especially ELD-M a lot. Or more precisely AB is averaging the BC, or using a lower Mach. However, for the vast majority of hunters and shooters, Mach 2.25 lines up better overall from muzzle to 800 yards plus, or if most ones shooting is beyond 800 yards, Mach 2 value works.
It doesn’t take much googling to find a common trend with people using ELD-M’s and AB is that they are having to screw with BC and data a bunch. Hornady is using Doppler like everyone doing it correctly.

On the flip side, in 4 DOF when not using Hornady bullets, windage outputs will be pretty wild from AJ- with Hornady bullets, it’s as expected.

Theres so many factors that i wouldnt say they are inflating the numbers. Speed, Twist, barrel grove, bore diameter, grove diameter, grove width etc will all impact how the bullet looks leaving the muzzle. A guy shooting a 6.5-300 weatherby and a guy shooting a 6.5 creed will see different BC numbers out of the same box of bullets. Thats why i true BC though because its the only input that i cannot measure myself. All other inputs are measured from my rifle at that time so unless my chrono or kestrel is giving incorrect data then thats the only factor that can be changed without fudging the numbers.

I've got no beef with those perspectives. I only know what I've observed. I don't compare several ballistic apps, and I don't use Hornady bullets much

when I did use Hornady at box BC values, and used MV supported by chrono, I was often left with mismatching dope. When I use AB values, it matches more consistently

And I do not mean to single out Hornady either.
Berger's 156 is box BC is 0.347 G7
AB library BC is 0.334
When I tested that at 1150yards, the AB library gave correct dope, the box BC did not.

 

[Formidilosus]

Theres so many factors that i wouldnt say they are inflating the numbers. Speed, Twist, barrel grove, bore diameter, grove diameter, grove width etc will all impact how the bullet looks leaving the muzzle. A guy shooting a 6.5-300 weatherby and a guy shooting a 6.5 creed will see different BC numbers out of the same box of bullets. Thats why i true BC though because its the only input that i cannot measure myself. All other inputs are measured from my rifle at that time so unless my chrono or kestrel is giving incorrect data then thats the only factor that can be changed without fudging the numbers.

But you are fudging the numbers- BC variation from rifle to rifle causes relatively minuscule changes in actual impact on targets. By the time you get to a range where a 10 point change can legitimately be seen, you are now dealing with huge variations from wind, drafts, angles, small errors in zero, etc. The amount of perfection across the board that must be attained to reliably see BC variation between rifles is obscene. I am not speaking to widely inflated BC numbers if yore, but known legit numbers now.

Changing a good BC number at 500, 600, 700, 800 , or even 900 yards is puzzling due the actual math. Please explain how you are seeing and adjusting the difference here, and how you believe this is effecting hits rates-

Both at 5K DA.

.600 G1 BC bullet at 3,000fps MV






.585 G1 BC at 3,000fps MV




A 15 point diffence in G1 BC causes-

1 inch difference at 800 yards

2 inches at 900 yards

3 inches at 1,000 yards.


A 15 point variation in G1 BC rifle to rifle is massive. Thats what happens when a bullet is barely stable- not between two stable bullets from different rifles. Even so, how many people can reliably, and consistently pick out even 3 inches in variation (.1 mil) at 1,000 yards and positively ID the cause as BC?


Not speaking to ELR here- inside the terminal range of bullets, you are lying to yourself to think adjusting a confirmed BC of a bullet is correcting the error.

 

[Formidilosus]

As a data point to illustrate that BC does not vary from rifle to rifle enough to functionally see.

The yellow is measured BC per shot during a 100 shot test, with a bullet that is known to have some of the widest BC variation from rifle to rifle. The red line points to a rifle that the bullet was barely stable: as in change the environment just a smidge and bullets might start hitting sideways.

 

[COPrecisionRifle]

you are correct i am fudging the numbers but those are the only numbers that are not directly measured from my rifle. So why is it better to fudge a known number (velocity) than a number that changes from rifle to rifle. The numbers you gave above i assume were at around the same speed. I dont know what mach value hornady is using for their supplied BC so if i run the .321(1.75 mach) or .351(2.25) mach thats the BC. They make a 3.5 inch difference in elevation at 800 yds so its a small difference i do agree but thats all that should need to be changed to true the data.

If u are going to account that difference to a bad zero, change in atmospherics, scope tracking, or any other factor then why would we change velocity over BC to account for the variability in data?

 

[Formidilosus]

If u are going to account that difference to a bad zero, change in atmospherics, scope tracking, or any other factor then why would we change velocity over BC to account for the variability in data?

With a legit MV fired with enough shots, and a legit zero, and the scope adjusting correctly to the most elevation dialed, and enough shots at distance to see the true cone, and no winds- there shouldn’t be any adjustment required.

Muzzle velocity is the largest variation from shot to shot, and in accuracy output- 1% at best. A 1% error at 3,000 fps MV (3,030fps) causes a 3 inch shift at 800 yards- 3 times larger than the realistic possible limit of BC variation from rifle to rifle.

 

[The Guide]

How many of these incorrect drops can be attributed to incorrect parallax adjustment resulting in aiming points not being in the correct position to prevent optical drift? Many people say that their drops are low at one range yet high at other ranges. This is the only thing I could come up with that would cause things to drift when you have measured inputs for every thing else. Parallax is the only thing in the system that is objective and cannot be measured or verified in the field with a tool. I've had situations where if a blinked a few times or adjusted my glasses the scope need to have a slight parallax adjustment before the shot.

Jay

 

[Okie_Poke]

With a legit MV fired with enough shots, and a legit zero, and the scope adjusting correctly to the most elevation dialed, and enough shots at distance to see the true cone, and no winds- there shouldn’t be any adjustment required.

Muzzle velocity is the largest variation from shot to shot, and in accuracy output- 1% at best. A 1% error at 3,000 fps MV (3,030fps) causes a 3 inch shift at 800 yards- 3 times larger than the realistic possible limit of BC variation from rifle to rifle.

Okay, probably a dumb question. But if this is true, why true anything? If it's not hitting in the "correct" spot at range, why adjust either BC or MZ instead of starting over and figuring out which of the "ifs" in that statement you've got wrong? Not trying to be argumentative here, just trying to learn---my only experience at ranges 600 yards and beyond involves the permissive use of sighters on a known distance range, so I don't have an opinion on this at all.

Edit: I guess maybe it's an ammo saving technique? If you've got to shoot 20 over a chrony to get a true avg velocity, and then shoot 20 at range to confirm your dispersion cone, why not just do that at the same time or avoid buying a chrony altogether?

 

[Formidilosus]

Okay, probably a dumb question. But if this is true, why true anything? If it's not hitting in the "correct" spot at range, why adjust either BC or MZ instead of starting over and figuring out which of the "ifs" in that statement you've got wrong? Not trying to be argumentative here, just trying to learn---my only experience at ranges 600 yards and beyond involves the permissive use of sighters on a known distance range, so I don't have an opinion on this at all.

Edit: I guess maybe it's an ammo saving technique? If you've got to shoot 20 over a chrony to get a true avg velocity, and then shoot 20 at range to confirm your dispersion cone, why not just do that at the same time or avoid buying a chrony altogether?

Your last paragraph has it. I only use a chrono now because the Garmin is easy peasy. Otherwise, legit zero, then shoot as close to transonic or terminal range as possible, and true MV. That results in correct data from muzzle to max range.


The whole issue is that BC variation from rifle to rifle results in less elevation error than you can see and measure until you get to well past terminal range of almost any bullet and cartridge combination. It’s ballistic masterbation- the flip side, is MV variation in chronos is at the limit that very solid shooters can see and detect.
So you have one variable that is not large enough to definitively see, and one that is- so which is more likely? A massive issue causing an BC variation that would almost always show itself at 100 yards; or normal error of a chronograph? People are getting hung up on “knowing” the MV die a chrono, and yet the chrono has an accepted +/- 1% at best.


All that aside, if you are using known and proven BC values for a bullet, using a Garmin chrono with 20+ shots for a legit average MV, and are having a legit error in data at 800 or 900 yards- you have an error somewhere else in the system. In almost all cases itisn’t the BC and it isn’t the MV that’s causing it.

 

[Okie_Poke]

Reading all of this got me curious. So I ran the 140 ELDM at 2700 fps through Hornady's ballistic solver using 4DOF, Mach 2.25 BC, Mach 2.0 BC, and Mach 1.75 BC. But instead of looking at inches I rounded to the nearest 1/4 MOA because I can't adjust a scope any finer than that.



Note on 4DOF: I used the "windless trajectory" value for drop so it would be apples-to-apples with the BC solver. If you put 0 wind vs a 90 degree wind vs a 270 degree wind into 4DOF, it will give you different elevation solutions, holding all else constant. By reporting windless trajectory it gives you the drop without that wind effect, which is what I think the BC solver is doing.

I don't really know what the take-away from this is, other than 4DOF is not following any of the BC curves (which Hornady has explained in one of their podcasts). But if Hornady's 4DOF is "correct" about the bullet's trajectory because it's based on the actual drag curve for that bullet, one would have to use a BC lower than the Mach 1.75 G7 to match drop at 1000 yards. Assuming you can shoot the 1 1/2 MOA difference at that range.

 

[Shortschaf]

Reading all of this got me curious. So I ran the 140 ELDM at 2700 fps through Hornady's ballistic solver using 4DOF, Mach 2.25 BC, Mach 2.0 BC, and Mach 1.75 BC. But instead of looking at inches I rounded to the nearest 1/4 MOA because I can't adjust a scope any finer than that.

View attachment 744225

Note on 4DOF: I used the "windless trajectory" value for drop so it would be apples-to-apples with the BC solver. If you put 0 wind vs a 90 degree wind vs a 270 degree wind into 4DOF, it will give you different elevation solutions, holding all else constant. By reporting windless trajectory it gives you the drop without that wind effect, which is what I think the BC solver is doing.

I don't really know what the take-away from this is, other than 4DOF is not following any of the BC curves (which Hornady has explained in one of their podcasts). But if Hornady's 4DOF is "correct" about the bullet's trajectory because it's based on the actual drag curve for that bullet, one would have to use a BC lower than the Mach 1.75 G7 to match drop at 1000 yards. Assuming you can shoot the 1 1/2 MOA difference at that range.

Can you chart that alongside 0.296 (AB value)

 

[Okie_Poke]

Can you chart that alongside 0.296 (AB value)

 

[Wiscgunner]

I trust my Velocity as it is a known measurement based upon results from accurate topend chrongraphs (MS v3 & Garmin). There should be no reason to lie to the computer about fake velocity numbers to make up for bad math on the software side. I use Trasol for my Centerfire as I find it more consistent beyond 1000 compared to AB or BallisticARC as Trasol uses different math formula that is less BC dependent.

For .22lr this has not work so well for me but with BallisticARC you can create your own custom curve my adding multiple BC's across multiple velocity bands and that way I was able to actually true my computer data to my real world results for the .22lr. If I recall correctly, I think I use 6 different BC/velocity bands out to 200 yards.

Neither rifle situation do I lie about my muzzle velocity as it is ludicrous to me to fake the one thing you do know.

Edited to Add:
It is very important to understand bullets do not have a BC number, bullets at a particular moment have a BC. Drag changes with speed. This BC value will change every millimeter that bullet changes speed. Using a single BC means your calculator can only be sorta accurate for a single arc range. A little high here, a little low there but mostly on for the range of that velocity. This works for most people and between the different ballistic solvers, they all work just fine inside about 800yrds. For ELR this doesn't work quite so well. The more velocity bands put into the ballistic solver the more accurate the bullet flight prediction will be. This is what custom drag curves are doing is plotting multiples, dozens, or even thousands of BC/velocity correlations along the predicted flight distance. This is where the BC based math models (the same used in phone apps, free computers and AB) are all the same and suffer this requirement.

Hornady 4dof and Patagonia (Trasol) both use different math.

If your centerfire long range is inside 800yrds, don't worry so much and just use chrono velocity and AB BC and move on with your life. If you are working outside of the norm then you may need to do more work. I'm my experience, most people that struggle in these medium ranges have incorrect scope height input, use mv off a a box and a "close enough" zero. Half ass effort with setup and half ass results down range.

 

[Lawnboi]

Any time I see someone having to ask about trueing I question whether it’s really necessary and I would also ask you to question whether you are trueing to an erroneous zero or to conditions.

Story, before I shot my very first match, I was at a 1000 yard range with heavy mirage, and trued my rifle, ended up having to raise my velocity. Never mind that I wasn’t shooting statistically relevant groups but what I ended up with was fudged data the next weekend in normal conditions.

With the tech we have now, and solid scopes, and solid rifles, and good loading practice/quality ammo, I don’t see how anyone needs to true anything out to the transonic range. And if you do need to true at 5 or 700 yards I’d be questioning what you’re really trueing, and suspecting something else going on.

This is not to say under certain conditions trueing isn’t needed. Just some food for thought on what we are really accomplishing.

 

[Formidilosus]

Any time I see someone having to ask about trueing I question whether it’s really necessary and I would also ask you to question whether you are trueing to an erroneous zero or to conditions.

Story, before I shot my very first match, I was at a 1000 yard range with heavy mirage, and trued my rifle, ended up having to raise my velocity. Never mind that I wasn’t shooting statistically relevant groups but what I ended up with was fudged data the next weekend in normal conditions.

With the tech we have now, and solid scopes, and solid rifles, and good loading practice/quality ammo, I don’t see how anyone needs to true anything out to the transonic range. And if you do need to true at 5 or 700 yards I’d be questioning what you’re really trueing, and suspecting something else going on.

This is not to say under certain conditions trueing isn’t needed. Just some food for thought on what we are really accomplishing.

Correct.