You Only Need to Know This If You Shoot Past 700 Yards!

jkupper

Well-Known Member
Joined
Jan 8, 2013
Messages
436
Location
Nebraska
jkupper, since you did not specify a muzzle velocity etc. let's say this is done at
2900 f/sec muzzle velocity, at sea level and std conditions.

View attachment 18342

Thanks, and that velocity is right around where I was wondering. I haven't gotten a load worked up yet, so I didn't know what to put for a velocity. So, the difference at 1000 yards would be about 3 inches, is that correct?

But, the difference becomes much more significant out a few hundred more yards. Definitely something to know! Thanks again!
 

Eaglet

Well-Known Member
Joined
Feb 2, 2005
Messages
2,779
Location
Nevada
If you want the most accurate results arguably you shoudn't be using BC's at all. For most low drag bullets the G7 is better than G1, but there are still significant differences between the predictions and reality. Look at Brian Litz's book in the back chapters where the match between G1 and G7 trajectories are compared to millimeter radar measurements of the actual velocity vs air density results. In most cases the G7 is a better match for "long range" bullets. There are some notable examples where the G1 is a better match. The 240 grain Sierra Matchking is an example. It's really not a VLD design even though it's a spitzer boatail.

Most of us don't have access to a range equipped with mm doppler radar and I don't know of any available ballistics programs which allow entering doppler radar results directly even if you have them.

You do have the option of doing your own shooting tests from your rifle and cartridges. It's more tedious than just relying on a computer output but you can use most modern ballistics programs to "curve fit" measured results to give better results than you're likely to get using manufacturers published G1 or G7 numbers. By better results I mean a better prediction of shot placement at various ranges using your handloads (or specific model of quality factory ammo). and your rifle in your environment. You still have to adjust for your local air density at the time you shoot and (perhaps) the temperature of your ammo at the time of firing.

Few shooters want to take the time and effort to get the most accurate results for "first shot" accuracy. For target shooter who are allowed sighters knowing the exact BC and exact air density makes little difference. For hunters, snipers, and some competition with targets requiring first shot hits at random targets and random ranges it may be worth the effort.

I have far more confidence in a set of range cards set up for my rifle and specific ammo for a range of air density derived from shooting tests made in the environment where I shoot than any computer generated results based on factory numbers for BC. You can make a good table over the supersonic range of a rifle with about 20 carefully fired shots. Certainly using G() functions and a ballistic calculator are useful just to put the shots on a target face so you can measure them. Wind deflection can be calculated from accurate drop measurements. Trying to measure wind deflection vs natural wind vectors in taking the drop measurements for the range card. Shooting over flat land in low wind will result in better quality drop measurements.

LouBoyd, I have a hard time fully agreeing with you. There's a lot of truth as it was in my grandpa's belief that his mule was better than my dad's 4x4 Willy's pick-up.
Of course mules have their place today as your way of going about it if you don't
have a good ballistics program to use.

We all understand the need to verify that our data being used is putting bullets on
target, but once that's done by field shooting, we have nothing but benefits when
using good ballistics programs.

I just love shooting at rocks of what ever at 1500 yards up-hill and down-hill (which by the way some wrongly believe that the correction is the same weather up-hill or down-hill), at what ever conditions, using spin drift and Coriolis corrections without having to do any calculations by hand and so forth. Seeing dust kicking off "right on target"... it's a thrill for me how precise the program I use can be. I know there are some geniuses out there that can do it in their heads but that's not for me nor many of us... :)

Again we're off topic!!!!
 
Last edited:

Bart B

Well-Known Member
Joined
Dec 25, 2005
Messages
2,763
Ballistic coefficients are a lot like rifling twist rates; calculating what's best for a bullet at a given velocity involves picking the right stuff to use. There's been all sorts of methods used and some are better than others.

My only experience in using calculated bullet drop down range then testing its accuracy has been with Sierra Bullets' software and their bullets. Shooting at 100 yards to get a ballistic zero, then lowering the sights an amount equal to bullet drop plus sight height above bore to get a shooting bore sight for the bullets previously chronographed speed was the first step. 'Twas always interesting that the muzzle axis never aligned 3.5" below the line of sight at 100 yards after doing this; proof the bullet's exit angle was different than the static bore axis angle for a shooting zero at 100. The atmospheric conditions would also be recorded for this zero.

On the range at 300, 600 and 1000 yards, come ups from that 100 yard zeros calculated for the atmospheric conditions using actual sight movmemts would be applied. First shot at each range was within 1/2 MOA of point of aim. So, seems Sierra's G1 based calculations were pretty close to reality; at least for the way I used them.

Some of Sierra's bullets have 4 or 5 BC's for different velocity bands. My aeronautical engineer nephew told me that airplanes also have different "drag" numbers for different speeds through the air. All of which is not well understood by me as Berger's single G7 BC's per bullet seem to be correct according to them. No doubt the formulas and standards used in the math is different.
 

phorwath

Well-Known Member
Joined
Apr 4, 2005
Messages
7,424
Location
Alaska
Most of us don't have access to a range equipped with mm Doppler radar and I don't know of any available ballistics programs which allow entering Doppler radar results directly even if you have them.

You do have the option of doing your own shooting tests from your rifle and cartridges. It's more tedious than just relying on a computer output but you can use most modern ballistics programs to "curve fit" measured results to give better results than you're likely to get using manufacturers published G1 or G7 numbers. By better results I mean a better prediction of shot placement at various ranges using your handloads (or specific model of quality factory ammo). and your rifle in your environment. You still have to adjust for your local air density at the time you shoot and (perhaps) the temperature of your ammo at the time of firing.

Few shooters want to take the time and effort to get the most accurate results for "first shot" accuracy. For target shooter who are allowed sighters knowing the exact BC and exact air density makes little difference. For hunters, snipers, and some competition with targets requiring first shot hits at random targets and random ranges it may be worth the effort.

I have far more confidence in a set of range cards set up for my rifle and specific ammo for a range of air density derived from shooting tests made in the environment where I shoot than any computer generated results based on factory numbers for BC. You can make a good table over the supersonic range of a rifle with about 20 carefully fired shots. Certainly using G() functions and a ballistic calculator are useful just to put the shots on a target face so you can measure them. Wind deflection can be calculated from accurate drop measurements. Trying to measure wind deflection vs natural wind vectors in taking the drop measurements for the range card. Shooting over flat land in low wind will result in better quality drop measurements.

Doppler radar is used to accurately identify bullet velocity throughout travel downrange. Accurate BC values can then be calculated based on these known accurate bullet velocities at different known ranges. Accurate BC values can also be calculated based on bullet time-of-bullet-flight measurements collected over long yardages, either by light sensing chronographs of acoustic sensing chronographs. Good ballistics programs can use these accurate BC values to determine accurate dope for shots under variable and changing environmental conditions, locations, directions of fire, and slopes that can be encountered while hunting at any location, altitude, and conditions of fire. It's difficult and tedious to prepare for these variable and changing factors some hunters encounter by attempting to use printed range cards developed by measuring drops over extended distance at a practice range. Range cards are great for hunting at the same location where you collected the measured drops. But they won't be nearly as adaptable and accurate after relocating to a hunting location 500 miles away and 6000 feet higher in elevation, while engaging a game animal up or down a 25 degree sloped mountainside. Thus the advantage of a good ballistics program, loaded with an accurate BC value and muzzle velocity for the bullet in use.

Confirming corrective dope for the actual shot on game is a great tactic if a hunter is setting up to ambush game at a specific location. One can then set up a large target where the game is expected to appear and take practice shots until the rifle is zeroed dead-nutz on before the game animal walks over to the location where the target had been previously set up. On my hunts (mountainous terrain), I can't often predict when or where I'll be setting up for the shot. My ballistics program is able to provide accurate dope no matter where the shot presents, provided I've entered accurate data, including accurate BC values.
 

elkaholic

Well-Known Member
Joined
Dec 4, 2008
Messages
10,091
Location
hauser, id.
Doppler radar is used to accurately identify bullet velocity throughout travel downrange. Accurate BC values can then be calculated based on these known accurate bullet velocities at different known ranges. Accurate BC values can also be calculated based on bullet time-of-bullet-flight measurements collected over long yardages, either by light sensing chronographs of acoustic sensing chronographs. Good ballistics programs can use these accurate BC values to determine accurate dope for shots under variable and changing environmental conditions, locations, directions of fire, and slopes that can be encountered while hunting at any location, altitude, and conditions of fire. It's difficult and tedious to prepare for these variable and changing factors some hunters encounter by attempting to use printed range cards developed by measuring drops over extended distance at a practice range. Range cards are great for hunting at the same location where you collected the measured drops. But they won't be nearly as adaptable and accurate after relocating to a hunting location 500 miles away and 6000 feet higher in elevation, while engaging a game animal up or down a 25 degree sloped mountainside. Thus the advantage of a good ballistics program, loaded with an accurate BC value and muzzle velocity for the bullet in use.

Confirming corrective dope for the actual shot on game is a great tactic if a hunter is setting up to ambush game at a specific location. One can then set up a large target where the game is expected to appear and take practice shots until the rifle is zeroed dead-nutz on before the game animal walks over to the location where the target had been previously set up. On my hunts (mountainous terrain), I can't often predict when or where I'll be setting up for the shot. My ballistics program is able to provide accurate dope no matter where the shot presents, provided I've entered accurate data, including accurate BC values.

Very well stated Paul! This is where I am right now. I'm trying to decide whether to put my $$$$ into ballistic programs "this year", or just spend more time fine tuning at my elk hunting stand and look to expand down the road? I have too many places to spend my $$$$:D.......Rich
 

Eaglet

Well-Known Member
Joined
Feb 2, 2005
Messages
2,779
Location
Nevada
Phorwath old buddy, glad you're still alive.

Take care of your self and your loved ones!

Regards,

Javier Moncada (Eaglet)
 
Last edited:

Bart B

Well-Known Member
Joined
Dec 25, 2005
Messages
2,763
After ones got all the ballistics figured out and zeros for every yard of range from here to eternity, judging the sight correction for cross winds is what's left.

Do you know how to adjust your scope's focus to see the mirage (heat waves) wrinkling across the field of view and estimate its speed across the bullet's path at different distances down range?

Which range band of wind has the greatest effect on drift; winds closest to you, half way to the target or closest to the target?

With a foot or more of drift per mph of consistant cross wind speed at ranges past 1000 yards, you'll need to be able to judge cross wind speeds very accurate. And the wind never blows across the line of sight uniformly all the way to the target. To say nothing of the fact that for a given wind speed across the ground, it gets faster for each foot above ground. How much faster depends on the terrain it's blowing across; less per foot above flat, smooth ground; more with vegitation such as brush and trees as well as other obstructions. Which means the wind's blowing faster on the bullet when its at its highest point in its trajectory. Then you'll also need to correct for the wind angle relative to the line of sight.

Getting zero's is about 20% of long range first shot hit success. The rest of it's correcting for crosswinds.
 

shortpants

Well-Known Member
Joined
Jan 26, 2011
Messages
619
Geez Bart is that it? You make it all sound so simple! J/K Knowing what you just said is true is what fascinates me about long range shooting. Seeing others finding success at it reminds me it's possible but reading what you just wrote and having many learning experiences myself keeps me scratching my head.
 

Bart B

Well-Known Member
Joined
Dec 25, 2005
Messages
2,763
Shortpants, it's really that simple. . . . .

Especially when one considers the fact that decent bullets flying through the air at 1500 yards drop about 2 inches per horizontal yard of travel. So getting the range to within 5 yards of reality means you may not miss your point of aim by more than 10 inches. That's assuming all the other ballistic stuff corrected for is absolutely exact.

The hard part's remembering all this stuff when you need to use it.
 

phorwath

Well-Known Member
Joined
Apr 4, 2005
Messages
7,424
Location
Alaska
Phorwath old buddy, glad you're still alive.

Take care of your self and your loved ones!

Regards,

Javier Moncada (Eaglet)

Thanks Javier, and the same to you. Glad to hear you're remaining active with your guns and gear, enjoying those long range shots, and putting CB1.0 to good use.

Paul
 
Top