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Seasoned Vet
 
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I know that ballistics are affected by many different things (barrel length, rifling, powder, bullet, temp., elevation...) Where can I find the constant for drop of an M-16A2 firing the military round, M-4, the new hypothetical rounds getting tossed around here and various 7.62 launchers?
This would be at sea level and a particular temp. obvoiusly.
I am looking for the constant you multiply by an exact range to get an offset for long range shooting. As many sources or numbers as I can get would be enough.
Thanks.
Go with God, but make Him walk the point.
If you load a mudfoot down with a lot of gadgets he has to watch somebody a lot more simply equipped - say with a stone axe - will sneak up and bash his head in while he is trying to read a Vernier. - Robert Heinlein
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Regular Joe
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Look it up in any reloading manual. Best one would be Sierra (check the spelling) Reloading or Hodgdon Powder Reloading Manuals. Drops are in the back of the book based on bullet weight and speed. So says my daddy.
"Lets kick this pig"
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Regular Joe
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Last Login: 10/31/2004 11:42 AM
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There is no constant as you know it. External ballistics is a MF to get perfectly accurate, we normally use an aproximation based on a drag function, G1.
I use the JBM ballistics website online calculator: It's here:http://www.mega.nu:8080/traj.html
You'll have to plug in the ballistic coefficients, bullet weights and other variables to get what you want. Sorry, but there's no graphing function that I'm aware of. You could use a graphing calculator but I don't know the formulas offhand that you'd need to enter. I just use the results, I'm not into the math part of the game. S/F...Ken M
"It's easy to be hard, it's hard to be smart"
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Seasoned Vet
Group: Past PNET Supporter
Last Login: 9/7/2005 7:22 PM
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Rick, here is a simple program from Norma that will help you compare external ballistics of several different cartridges:
http://www.norma.cc/htm_files/javapagee.htm
As an example, if you go to the 'define your own bullet' tab and enter the specs for this 6.5mm Grendel cartridge (123gr, .547 bc, 2750 fps, and 200 yd zero), you will see that at 600 yards the bullet has a retained velocity of 1,834 fps, a retained energy of 920 ft lbs, a time of flight of .803 seconds, and a bullet drop of -75.7 inches from line of site.
You can also load this free program on your machine called Winball:
http://www.snipercountry.com/ballistics/software/WinBall.zip
If you want to do a more indepth study, check these links out:
http://www.exteriorballistics.com/ebexplained/index.cfm
http://www.nennstiel-ruprecht.de/bullfly/index.htm#Contents
http://www.snipercountry.com/ballistics/
Enjoy.
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Regular Joe
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Rick, there isn't a constant because the formula for ballistic drop (even if you ignore drag) is a second degree polynomial. You're plotting the acceleration due to gravity (down) against time. In the real world you can't ignore drag and other factors. Tanks (even the later M60's) have a ballistic computer that takes into consideration crosswind, altitude, range, round selected, at least.
Most manufacturers post bullet drop at specific ranges from 100 to 600 yards for their rounds at ballistic standard conditions. For example, Federal (www.federalcartridge.com) posts the following for American Eagle 55 gr FMJ boat tail:
50 yards -0.3"
100 nil
200 -2.5"
300 -9.9
They also give drift in a 10 mph crosswind, velocity, energy, etc. The reloading manuals mentioned above allow you to "roll your own." But AR's are used so often in competition that the trajectories for any given commercial load are easy to find.
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Seasoned Vet
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But what about the charts guys tape to their buttstocks? It has a little curve and they just click or offset for a given range.
I am assuming that this is at a fixed elevation, level shooting, about 80 degrees F with zero wind. This would just be for a service rifle firing issued ammo.
I'm sure I can dig it up with the comps and charts ya'll gave.
Thanks.
Go with God, but make Him walk the point.
If you load a mudfoot down with a lot of gadgets he has to watch somebody a lot more simply equipped - say with a stone axe - will sneak up and bash his head in while he is trying to read a Vernier. - Robert Heinlein
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FNG
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Rick, Here is the standard given as it appears in Speers reloading manual #13.It is listed as the standard ballistic coefficients as defined by the U S Army Ballistic Research Laboratory at Aberdeen Proving Grounds in Maryland. Altitude: sea level Tempurature: 59 F/(15 C) Pressure: 29.53 Hg/(750 mm Hg) Relative Humidity: 78% Air Density: 0.0751 lbs/foot(to third power)(0.001203 grams/cc) The manual then goes on to explain the VERY complicated formulas used to derive specific ballistic data from the above stated standards.To list it all here would take to long,But RCBS now offers ballistic software that could help you take the headache out of this thing.The program is called RCBS.LOAD.You can get it from most gun dealers who deal in reloading.
HIT THE HOLE,POLE MAN,HIT THE HOLE!
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Regular Joe
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Last Login: 2/14/2008 2:14 PM
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>>But what about the charts guys tape to their buttstocks? It has a little curve and they just click or offset for a given range. I am assuming that this is at a fixed elevation, level shooting, about 80 degrees F with zero wind. This would just be for a service rifle firing issued ammo. I'm sure I can dig it up with the comps and charts ya'll gave. Thanks.
If you go to most cartridge manufacturer websites, they have some ballistic data. They will usually list bullet drop with the rifle zeroed at 100 yards for 200 to 500 or 600 yards or meters. They will also give the crossways drift in a 10 mph breeze, usually.
For example, Federal American Eagle 55 gr FMJ is at:
http://www.federalcartridge.com/ammocat20.asp?act=detail&id=3&firearm=2&shelltype=
Zeroed at 200 yards, that shows a bullet drop of +1.3" at 100 yards, -6.1" at 300, -18.3" at 400, and -37.8" at 500.
Hope that helps.
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