About Ballistic Coefficient

[Koda]

Custom turrets are great, absolutely.

yeah, but I have to give them the bullets BC. So Im just questioning how accurate advertized BC is.

I think for under 500yds your probably right the advertized is close enough, but Id hate to start having issues with a custom turret if some day my skills grew past 500...

 

[Kruel J]

yeah, but I have to give them the bullets BC. So Im just questioning how accurate advertized BC is.

I think for under 500yds your probably right the advertized is close enough, but Id hate to start having issues with a custom turret if some day my skills grew past 500...

You're always going to have to fine tune it………

 

[titsonritz]

I'm confused, ballistic coefficient has nothing to do with your rifle, it is a mathematical equation used to evaluate the bullet in terms of external ballistics and flight characteristics in the real atmosphere. Here is the formula...

https://www.sellier-bellot.cz/en/products/ballistic-coefficient-calculation/

 

[Koda]

I'm confused, ballistic coefficient has nothing to do with your rifle, it is a mathematical equation used to evaluate the bullet in terms of external ballistics and flight characteristics in the real atmosphere. Here is the formula...

https://www.sellier-bellot.cz/en/products/ballistic-coefficient-calculation/

aaack. If thats the kinda math I gotta use I'll never figure it out.



I will just shoot for drops and write down my clicks.

 

[titsonritz]

aaack. If thats the kinda math I gotta use I'll never figure it out.

View attachment 1444870

I will just shoot for drops and write down my clicks.

Yep, maph is hard...


...and racist.

 

[RX-79G]

aaack. If thats the kinda math I gotta use I'll never figure it out.

View attachment 1444870

I will just shoot for drops and write down my clicks.

You don't have to figure it out. You just use the ballistic calculator backwards, changing BC until you get your observed velocities in the same conditions. The calculator... calculates the BC for you.

You don't even need two chronographs. Just get samples at both ranges.

 

[Koda]

You don't have to figure it out. You just use the ballistic calculator backwards, changing BC until you get your observed velocities in the same conditions. The calculator... calculates the BC for you.

You don't even need two chronographs. Just get samples at both ranges.

I'll give that a try and see how that compares to the advertized BC. The question I have with that is id be using my drops (moa) instead of my velocity because my velocity (average) doesnt change.
Ie: if it takes me 12 clicks at 300yds I adjust the BC in the calculator till the drops reads what Im using.

 

[RX-79G]

I'll give that a try and see how that compares to the advertized BC. The question I have with that is id be using my drops (moa) instead of my velocity because my velocity (average) doesnt change.
Ie: if it takes me 12 clicks at 300yds I adjust the BC in the calculator till the drops reads what Im using.

I don't follow. I'm talking about using an online ballistic calculator, the range conditions, the bullet weight and the chrono velocity at two distances from the muzzle.

If you want to use muzzle velocity and drop, you had better get scope height measure perfect. Of course, that makes me wonder about custom turrets - do you tell them what your scope height is, or is it not supposed to matter? High scopes make it appear there is less drop.

 

[Koda]

I don't follow. I'm talking about using an online ballistic calculator, the range conditions, the bullet weight and the chrono velocity at two distances from the muzzle.

If you want to use muzzle velocity and drop, you had better get scope height measure perfect. Of course, that makes me wonder about custom turrets - do you tell them what your scope height is, or is it not supposed to matter? High scopes make it appear there is less drop.

online ballistic calcs dont use two velocity inputs, only muzzle. And yes a very accurate scope height is required.

Heres the calc I use for my handload devolopment. The bookmark is my last range session results. I went out to 200yds and only needed 3 clicks (1/4moa) to hit bullseye but the calc says Im dropping -2.23inches. 3 clicks is only 1.5" at 200yds... so I think the advertized BC is off.

ShootersCalculator.com | Ballistic Trajectory Calculator

Calculates the ballistic trajectory of a bullet fired from a rifle, handgun or other firearm. Produces a ballistic trajectory chart and table that shows the drop, velocity, kinetic energy, windage, and trajectory of a bullet.

shooterscalculator.com

 

[RX-79G]

online ballistic calcs dont use two velocity inputs, only muzzle. And yes a very accurate scope height is required.

Heres the calc I use for my handload devolopment. The bookmark is my last range session results. I went out to 200yds and only needed 3 clicks (1/4moa) to hit bullseye but the calc says Im dropping -2.23inches. 3 clicks is only 1.5" at 200yds... so I think the advertized BC is off.

ShootersCalculator.com | Ballistic Trajectory Calculator

Calculates the ballistic trajectory of a bullet fired from a rifle, handgun or other firearm. Produces a ballistic trajectory chart and table that shows the drop, velocity, kinetic energy, windage, and trajectory of a bullet.

shooterscalculator.com

Why aren't you getting this? Online ballistic calculators don't tell you BC - it's an input. If you want it as an output you have to use the program backwards, forcing it to match observed velocities by changing the BC input.

Like this (fake numbers):
Predicted: Muzzle vel: 3000,Weight 160gr, BC: .8, 200m velocity 2640, 58F, 29.82
Actual: Muzzle vel: 3000, Weight 160gr, BC: .8, 200m velocity 2450 58F, 29.82

Then you change the BC number until the calc says:
Muzzle vel: 3000, Weight 160gr, BC: .72, 200m velocity 2450 58F, 29.82

So if you did everything else correctly, the only way to end up with 2450fps is if your BC is actually .72, not the advertised .8. Then you know. Or, you can do it with predicted vs actual drop.

 

[Koda]

Why aren't you getting this? Online ballistic calculators don't tell you BC - it's an input. If you want it as an output you have to use the program backwards, forcing it to match observed velocities by changing the BC input.

Like this (fake numbers):
Predicted: Muzzle vel: 3000,Weight 160gr, BC: .8, 200m velocity 2640, 58F, 29.82
Actual: Muzzle vel: 3000, Weight 160gr, BC: .8, 200m velocity 2450 58F, 29.82

Then you change the BC number until the calc says:
Muzzle vel: 3000, Weight 160gr, BC: .72, 200m velocity 2450 58F, 29.82

So if you did everything else correctly, the only way to end up with 2450fps is if your BC is actually .72, not the advertised .8. Then you know. Or, you can do it with predicted vs actual drop.

Why arent you getting that Im getting this? ;P

Im talking about exactly what you just described. "tweaking" the BC input till the velocity and drops match my actual results.

 

[drstrangelove]

Why arent you getting that Im getting this? ;P

Im talking about exactly what you just described. "tweaking" the BC input till the velocity and drops match my actual results.

That is completely ok and is what one of my friends who is a top PRS shooter recommended to me exactly, although you should be doing chrono at the muzzle and inputting that correctly. The downside to this is there will be a miscalculation in wind drift output on your ballistic calculator.

 

[ORhutner]

To add to this I want to order a custom turret dial and while I might not need to shoot past 500yds right now I want it to be accurate at any distance.

I am not a fan of custom dial turrets. They are only correct for a point in time. The internal ballistics of your rifle are going to change over time and rounds down range making your custom dial no longer accurate. I would get a good ballistic app like Applied Ballistics and use the super computer in your pocket (aka cell phone) to generate your dope card. Then you can adjust your dope for the internal and external ballistic changes you encounter.

The best money I ever spent on long range shooting was taking a good intro to long range class. It will accelerate your journey, remove a lot of the mystery, eliminate the frustration and quickly get you competent to 1,000 yards.

 

[Koda]

I am not a fan of custom dial turrets. They are only correct for a point in time. The internal ballistics of your rifle are going to change over time and rounds down range making your custom dial no longer accurate.

Ive heard about this and as far as I know only throat erosion changes things then maybe altitude or environment. Im aware of the negatives but its what I got and most of my hunting is under 300yds.
I get a free custom dial with my scope so theres that.

 

[gmerkt]

It's my belief that all manufacturer data are estimates, however methodically and scientifically arrived at. Due to the many variables that present themselves when the products get into the hands of the users. So velocities, BC's. etc. are guidance rather than gospel.

My interest in firearms is almost purely recreational. I'm sure some people enjoy mathematic calculation just for the fun of it, but I'm not one of them. Sure, some math comes into reloading and a basic knowledge of the principles of physics helps. The last time I got into ballistics, I got sidetracked by the concepts of precession and nutation; then I got off on a tangent (pun intended) on astronomy and never got back to ballistics.

 

[Kruel J]

@Koda are you planning on shooting from a vise? If not, YOU will cause more variation to your shots than any BC anomalies.

 

[Koda]

@Koda are you planning on shooting from a vise? If not, YOU will cause more variation to your shots than any BC anomalies.

Nope. I don't own a vise.
My options are: bipod, prone, portable shooting bench with front rest.

For my first time going to 500 I'll probably start with the portable bench.

 

[ORhutner]

A good bipod, proper rear support bag and correct form will have you shooting to the accuracy capability of your rifle and load in the prone position. When you really get everything dialed in, you will be able to stay on target and spot your own shots. A great resource for those getting into long range is the knowledge provided by the Modern Day Sniper group. They have a lot of unpaid information and videos floating around the interwebs.

 

[Koda]

A good bipod, proper rear support bag and correct form will have you shooting to the accuracy capability of your rifle and load in the prone position. When you really get everything dialed in, you will be able to stay on target and spot your own shots. A great resource for those getting into long range is the knowledge provided by the Modern Day Sniper group. They have a lot of unpaid information and videos floating around the interwebs.

It's been a very slow crawl for me having to start over with rifle builds up for it, then learning handloading, but eventually will get to where I can shoot out to 500yds maybe 600 if I can. I will get there with practical positions hunting, bipod, backpack, shooting sticks.
For now to start I just want to ring my gong at 500 however...


I'll check out the Modern Day videos, thanks for the tip.

 

[Nosferatu]

Bullet manufactures use doppler radar to measure and calculate BC. Of course environmental conditions and actual velocity will affect it. The BC changes as it loses velocity downrange. Math will tell you this change. It's as accurate as the data you feed into it. If your wind, humidity and pressure instruments aren't up to snuff, none of the other data matters much either.

The Labradar chrono is the only one I know of that uses some sort of radar to measure velocity. I'm not sure if it spits out a BC estimate though. Might be worth investing in if you're looking for that kind of detail.

For me, using bullet makers estimated published BC along with my own chrono data, Kestrel readings and ballistic calculator has given me as good of results as I'm capable of taking advantage of even beyond 500 yards. No amount of data or equipment is going to make me shoot better, just more practice, which I don't do enough of anymore.

Some light reading while you're on the throne: https://arxiv.org/ftp/arxiv/papers/1608/1608.06500.pdf