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-   -   A math question of sorts (http://www.firearmstalk.com/forums/f18/math-question-sorts-20512/)

Hot Sauce NARC 11-28-2009 05:21 AM

A math question of sorts
 
lets just say i want to shoot 500 yards with my 308.

the ballistics table says the bullet will drop 51.5 inches at 500 yards

The hornady ballistic calculator says at that distance i will need to come up 9.9 MOA. I have calculated that this will only be 7.7 clicks up from a 200 yard 0 on my 1/4 MOA Leupold VARI X 3

So why is this calculator telling me the bullet will drop 51.5 inches at 500 but then it tells me i will only need to come up 9.9 MOA im missing something here. Im sure one of you had sone this a few more times than me and can help me understand how it all works.

mrm14 11-28-2009 07:35 AM

O.K. I have never used these ballistic calculators on the internet for drop because I spent a few $$$ to go to a school to learn this stuff. ( 2 days in class room and 2 days on range with personal insturctor) I will be attending another class in March 2010 for more advanced instruction. With that being said; Welcome to the world of long range shooting. I kinda' know your going to go to 1000 yards. I use a chronograph to determine my muzzel velocity on my ammo and I use a Kestral 4500np to determine the weather specs I need to calculate. I did look at the Hornady ballistic calculator however after reading your post. Several things you need to put into these factroy ballistic calcualtors or to figure to do the math yourself are as follows. Aside from caliber you need to know the ballistic coefficient for the bullet, the grain weight of the bullet your using, the muzzel velocity in fps of the bullet, the temperature, the barrometric pressure, your true sight height, the wind speed, and your zero range which you should have a zero at 100 but your zero is O.K. at 200 with this calculator. One thing not asked on the calculator is relative humidity which makes a diference in drop as well. Also 1 minute of angle adjustment in a 1/4 MOA scope is 4 clicks. Description in this Hornady calculator which I assume would require brand of ammo and factory named type, bullet weight in grains, and bullet type I belive will auto fill in some of the other "boxes" in this calculator which should make it somewhat easier on particullary the muzzel velocity.
All this info is critical to calculate your external ballistics and to have these calculations somewhat accurate.

As far as in field real time weather info device look up the Kestral 4500np thats what I use and it works well. Also It's kind of a cool device to have when in the "outback" on longer term camping trips. Also, instead of keeping my data written on paper notes, I use a ASUS heavy duty PDA loaded with the ballistic software I need to keep my info.

Hot Sauce NARC 11-29-2009 05:54 PM

thanks mrm14:

i was on the web after that post and i found a more advanced calculator that asks for alot more factors it gave me my click values on 168gr FGMM out to 500 yards as well as my windage "dope"

I went out yesterday and it was almost spot on. it was one or two clicks off on elevation but but the wind was stedy at about 8mph and gusting to about 20 so it was kinda hard to figure windage for both stedy wind and gusts but i had fun. Range report to follow.

mrm14 11-29-2009 11:03 PM

Quote:

Originally Posted by Hot Sauce NARC (Post 191929)
thanks mrm14:

i was on the web after that post and i found a more advanced calculator that asks for alot more factors it gave me my click values on 168gr FGMM out to 500 yards as well as my windage "dope"

I went out yesterday and it was almost spot on. it was one or two clicks off on elevation but but the wind was stedy at about 8mph and gusting to about 20 so it was kinda hard to figure windage for both stedy wind and gusts but i had fun. Range report to follow.

What ballistic calculator did you find? I'm really oblivious to them.
Did you look at the Kestral weather device? It is expensive but even with these internet calculators they will give you current real time info to enter. As you may go further out in distance for shooting, their value for what you may be trying to do is invalubale.

Hot Sauce NARC 11-29-2009 11:16 PM

I actually found a couple online and one app for my phone which was free. Knight armamnet makes a badass one for Iphone for like 5 dollars but they dont make it for andriod yet.

these both got me pretty close:
External Ballistics Calculator

JBM - Calculations - Trajectory (Simplified)

Dillinger 11-29-2009 11:20 PM

Hot Sauce - While it's not free, this is BY FAR the best source for information on ballistics. This guy, Art Lejsa, bascially re-wrote the mathmatical formula on what a bullet does in flight.

Pejsa Rifle Ballistics: Art Pejsa's Rifle ballistics software and books

This is the best software that we have tested to date. The most accurate.

Chey Tac's Intervention system is on my list, but at the price of just the software, I need to try and blackmail someone at SHOT to get the Military Copy. :cool:

JD

mrm14 11-29-2009 11:39 PM

Hot Sauce- Check this out Kestrel 4500 Pocket Weather Tracker – Nielsen Kellerman

It may not be an issue for you now at 500 but will become a necessity towards 1000.

Hot Sauce NARC 11-30-2009 02:47 AM

thanks guys

im going to keep shooting this rifle and my savage if they ever send it back and i may just sell both of them and some other things and have somthing built (im thinkin 260 rem) that will necessitate such equipment and software.


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