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Computer Help

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Old 01-23-2013, 11:59 AM
Junior Member
Join Date: Apr 2005
Posts: 6
Computer Help

I am having trouble getting my computer to match my actual trajectory.

.284 winchester , winchester brass, 162gr AMAX, 50.0gr RL 17, Federal match primers.

The story:
I fired a five shot group at approximately 565 yards with a 220 yard zero. I established the range by milling the target with a mill-dot master. My group center was about 7.5 inches high, with about 2.5 inches vertical dispersion and 3.5 inch total group size. I had 34 clicks dialed on the scope w/ 1/4 minute clicks. Based on the difference between my POI and dope the best match in Knight Bullet Flight had me at around 3150 FPS, which is outlandish with that cartridge and powder charge. However, I set up a clay pigeon gragmetnt (1in. X 3 in. set up vertical) and a small rock (maybe 1.5X1) at around 60 yards. I referenced the dope from bullet flight, and first round hit both, chopping the clay pigeon fragment neatly in half. However, I then setup paper at 120 yards, milled the target, referenced bullet flight again, and now I was about 1.5 inches high of where the computer said I should be with a three shot group around .5 MOA. Sooooo.......

Bullet Flight (with Litz BC) was obviously wrong, since it gave me the wrong dope and a silly velocity, so I went home and put everything into Gseven. This however, gave me the same result as bullet flight. My next thought was that I ranged wrong, because with a shorter range Gseven gave me a corrected velocity of around 2930, which is more what I would expect. So I went back to the range and did a similar set of tests, with two guys ranging the target in both mils and MOA, and got the same results. Went home and plugged the result into Gseven to correct for velocity and got 3144, which I don't believe.

So: can someone help me jive my actual results with some computer, somewhere...'cause I'm trying to shoot my first tactical comp in two weeks.

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Old 01-23-2013, 12:29 PM
Gold Member
Join Date: Aug 2011
Location: Lynchburg, TN
Posts: 735
Re: Computer Help

My first thought is that you need an accurate chronograph and laser range finder. Then you can plug correct info into your ballistic program. It still may not match your drop tables exactly but you can make it match by manipulating the velocity or BC.
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Old 01-23-2013, 08:38 PM
Silver Member
Join Date: Dec 2007
Location: sebastopol, ca.
Posts: 418
Re: Computer Help

I have the same issue with my 6.5x.284. Chronograph reads 2930 and adjusted to 3100 on JBM to calculate the drop correctly.
Very frustrating. My chronograph is a CED and my rangefinder is a Leica 1200.
My group was under 1/2 MOA.
Looks like my findings at 500 yards are basically the same as yours. 200 fps seems a ridiculous amount to need to adjust.
Have you shot farther to check your drop with your new velocity numbers?
I am very interested....
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Old 01-24-2013, 04:59 PM
Junior Member
Join Date: Apr 2005
Posts: 6
Re: Computer Help

No, I think I can get out to about 700 in the sand pit where I am shooting. I can get a thousand if I go a range nearby, for which I MIGHT have an opportunity in Feb. I would be surprised if my BC was too far off since I am using Brian Litz' BC for the 162 AMAX. My thought is that it might be time for ATRAG software and a trip to the thousand yard range for truing at transonic distance as recommended with that software. Meanwhile I think I will be collecting data and making a dope card old school style until I get that squared away.
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Old 01-24-2013, 07:58 PM
Gold Member
Join Date: Jul 2010
Location: Mount vernon, OH
Posts: 670
Re: Computer Help

Make sure your sight height is correct. In my experience using Brian Litz data with my shooter app and Kestral has been dead on.

"Let glorious acts more glorious acts inspire,
And catch from breast to breast the noble fire!
On valour's side the odds of combat lie,
The brave live glorious, or lamented die;" - Iliad, Book V
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