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

 
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  #15  
Old 02-17-2013, 07:54 PM
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Location: Nebraska
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Re: You Only Need to Know This If You Shoot Past 700 Yards!

Quote:
Originally Posted by Eaglet View Post
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.

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!
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  #16  
Old 02-17-2013, 11:12 PM
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Re: You Only Need to Know This If You Shoot Past 700 Yards!

jkupper,

yes, that's correct.
__________________
-----------------------------

-----------------------------
HEBREWS 13:8
Jesus Christ the same yesterday, and to day, and for ever.

Our Lord Jesus said that as it was in the days of Noah and
also as it was in the days of Lot so it shall be in the days...
It's happening again!!! God sent to us His prophet, and His Word
to this generation and we once more are rejecting it as was prophesied!!!

---> As promised, God Sent His Prophet to us!
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  #17  
Old 02-18-2013, 01:20 AM
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Re: You Only Need to Know This If You Shoot Past 700 Yards!

Eaglet,

Great info, and thanks for posting!
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  #18  
Old 02-18-2013, 07:49 AM
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Re: You Only Need to Know This If You Shoot Past 700 Yards!

Quote:
Originally Posted by LouBoyd View Post
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!!!!
__________________
-----------------------------

-----------------------------
HEBREWS 13:8
Jesus Christ the same yesterday, and to day, and for ever.

Our Lord Jesus said that as it was in the days of Noah and
also as it was in the days of Lot so it shall be in the days...
It's happening again!!! God sent to us His prophet, and His Word
to this generation and we once more are rejecting it as was prophesied!!!

---> As promised, God Sent His Prophet to us!

Last edited by Eaglet; 02-18-2013 at 09:40 AM. Reason: corrections
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  #19  
Old 02-18-2013, 08:01 AM
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Join Date: Dec 2005
Posts: 2,114
Re: You Only Need to Know This If You Shoot Past 700 Yards!

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.
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  #20  
Old 02-18-2013, 12:54 PM
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Join Date: Apr 2005
Location: Alaska
Posts: 3,512
Re: You Only Need to Know This If You Shoot Past 700 Yards!

Quote:
Originally Posted by LouBoyd View Post
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.
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  #21  
Old 02-18-2013, 01:26 PM
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Join Date: Nov 2012
Location: Green River, Wyoming
Posts: 423
Re: You Only Need to Know This If You Shoot Past 700 Yards!

thanks!
Being OCD like I am this will surely help
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