Range Report noobie question on ballistic discrepancy

shopgun

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Oct 29, 2008
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Sure hope someone can help me with this, got me stumped.Rifle is a Rem 700, 243 win , 24" bbl, Leupold mk 4 6.5x20. Hornady 105 amax chrono'd @ 3000 fps. i zero'd at 100yd and then shot at 200, 300, 400 and 500. JBM shows -2.9@ 200, -10.7 @ 300, -24.1 @ 400 and -44 @ 500. I went the following adjustments to hit point of aim. + 6 clicks at 200 ( 3") + another 8 clicks at 300 (9"). + another 12 clicks @ 400 (21"). so far my results track pretty close to data for that bullet at 3200 fps, which I am definatly not making. The real surprise came at 500. I only needed 6 clicks (7.5") to hit POA. When I should have needed approx. 16. I did this again, starting with the 100 yd zero and back out to 500 with exactly the same results. What am I missing? as much as I'd like to ,I don't believe I've got a magic rifle. Thanks in advance for your help.
 

Lindy

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Re: noobie question on ballistic discrepancy

First of all, stop thinking in clicks or inches. It just gets confusing. The scope adjusts in angles, in your case, MOA. Think only in MOA, and run JBM again to get an output in MOA.

So, from what you're saying, from a 100 yard zero, is that your actual dope looks like this:
<div class="ubbcode-block"><div class="ubbcode-header">Code:</div><div class="ubbcode-body ubbcode-pre" ><pre>
Yards MOA
200 1.5
300 3.5
400 6.5
500 8.0
</pre></div></div>

Well, 44 inches at 500 yards is 8.4 MOA, so you're only nominally off less than a half MOA.

Not much error. And did you put the temperature and barometric pressure you shot in into JBM? If so, how did you measure them?

You might find this interesting:

Sources of Ballistic Program Inaccuracies
 

shopgun

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Oct 29, 2008
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Re: noobie question on ballistic discrepancy

Thanks for your reply. Sorry if I didn't make myself clear and I will work to think in MOA.
so, let me try again. I am using a multiplier of 1.0472 to convert inches to MOA. My actual dope is 200 yd-3"or 1.43moa. at 300 -9" or2.86 moa. at 400 -21" or 5 moa. this all pretty close to this bullet at 3200 fps. But it's the 500 yd data that has me stopped. From 400 to 500 I only had a drop of 7.5". That's a TOTAL drop of 28.5 "or 5.44 moa (if I have the moa thing correct) from a 100 yd zero to 500 yd. As I said, I have fired this twice with the same results. Just can't figure the dramatic difference in my fired results and the data from 400 to 500.
 

BobinNC

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Jan 31, 2009
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Re: noobie question on ballistic discrepancy

Here what I ran using JBM, and the G7 BC for your bullet.

Calculated Table
Range Drop Drop
(yd) (MOA) (in)
0 *** -1.9
100 -0.0 -0.0
200 -1.2 -2.5
300 -3.2 -10.0
400 -5.5 -23.1
500 -8.2 -42.7
600 -11.1 -69.8
700 -14.4 -105.5
800 -18.0 -151.2
900 -22.1 -208.5
1000 -26.7 -279.5

If you claim your only dropping .44 MOA from 400 to 500 yds, then something is very wrong, not with your bullet, no magic there, but your calculations must have a error. Either your chrono is reading wrong, or your ranges are incorrect.

Your data shows the bullet getting faster and flatter as the range increases. Which is not in line with the laws of physics. Is your target range level with your shooting position?

Bob