JBM ballistics drop table ???

CaptnC

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On the last day of a Aoudad sheep hunt over the weekend I used the program to hit a 6oz coke can at 600 yards...canyon to canyon over a deep ravine.

I used their program all the time and it works if everything is correct.

When we were getting ready for the hunt I worked up a super accurate load for my wife's 6.5 Creedmoor using Barnes 120gr TTSX (IIRC). We couldn't use her rifle for long range shots because it was way off.

I suspect Barnes BC might be the problem. I had used my Magnetospeed on both rifles and my 6.5-06 was spot on with 130gr Sierra Game Changers. But her Creedmoor was way off. First time I've had one off like that 400 yards.
 

PApa Black

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May 23, 2012
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I did a drop table for my 6.5 creedmoor and then went out and shot it at 300 yards. According to my velocity, correct BC, and other pertinent info it says my drop at 300 yards should be 12.9 inches. It is actually 10.5 inches. Does my 20 MOA rail factor in or what else could be the problem? Thanks in advance.
Shoot a 300 or 400 or 500 yard drop with a 100 yard zero. Then change the velocity in the Input to match the drop. The drop does not lie. I always use a 500 yard drop w ith 100 yard zero.
 

Pro2A

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No it’s off your zero. You rail just gives you more travel in the erector of the scope.

chances are you muzzle velocity is off if all else is correct. BC isn’t even worth looking at as it doesn’t come into play until around transonic.

You need to change the muzzle velocity until it matches your 2 and 300y drop.
Au contriere, BC.....the propensity to retain velocity.............is pertinent all the way from the end of the barrel to impact. However, BC varies continuously with velocity. Most BCs are listed as a single value, typically selected from the drag curve by manufacturers at the highest value for Marketing bragging rights and consumer confusion and duping. Using a CDC (Custom Drag Curve) can provide much more accurate ballistic data. You shared....this was my expectations; this is what I observed.......two numbers. With no more info than provided, it's almost impossible to answer your question. Every answer, including mine, is a SWAG (Silly Wild
*** Guess). Was this observed deviation only for one group or was it verified repeatedly? You only mentioned vertical deviation. What was horizontal data? At 100 yds, it is mostly the rifle characteristics, ammo ES/SD, and shooter technique causing variation. As distance grows, environmental variables and bullet flight characteristics enter. Don't assume that a digital readout of a chrono is true. What chrono? Verified setup, accuracy of chrono? One shot or a statistically valid set? What are the ES and SD for the ammo? First, triple check all the input values to your ballistic program, including unit consistency. That's where deviations often begin. Do you have some variables turned off in the ballistic program? The bullet doesn't disregard any variable. What is the verified rifle performance envelope...0.25 or 1.5MOA? Right there is an expected 0.75 to 4.5"probable envelope at 300yds. What was your accuracy and precision at 100 yd zero? A perfect one hole 10-shot group....or 1"...aw, that's good enough. Scope tracking....is it a knocked around old Tasco or a verified precise tracking TT/SB/NF?? The shooter is usually the biggest variable.......recoil management, trigger technique, parallax adjustment, cant, and on, and on, and on. What is your experience? How much have you shot?.....beyond 100yds? Each variable contributes a an increment to the total deviation observed. Establish a reliable base at 100 yds. Then, begin pushing out inconsistencies. That's what makes shooting so interesting. Every trigger squeeze has a different set of variables. Always trust the bullet. The bullet always knows. The bullet never lies. But, it's all those sneaky variables the bullet pals around with ya gotta watch. As Dad always warned, show me your pals and I'll show you where you'll end up. Same with the bullet. The bullet is truth, but Consistency is King,
 

michael569

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Feb 6, 2018
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If your bullet does not travel a path parallel to the chronograph then you MV will be off.
 

dfanonymous

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Jul 16, 2016
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Wait a minute, Berger says: "it’s better to true MV 10% under transonic"?
The only way to measure transonic muzzle velocity is with a transonic load. Perhaps with a cartridge for a suppressed gun. If you meant downrange flight times all the way out through transonic, that sounds like a good thing for Berger to setup & do.

I'll repeat again for everyone else; Do not LIE to your software.
For every input that you actually know, enter the truth.
For good bullet path prediction you need to know bullet BC, the air density standard that BC is based on, your local air density parameters, your muzzle velocity, and your sight parameters.
Don’t try to be a wise ***. I was giving you the benefit of the doubt to understanding the conversation be talked about, transonic range for a given load to a given cartridge. I speak the slang of my people for people who commonly understand.
I can go on. True your stuff.
 

foul bore

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Feb 1, 2016
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I think I figured it out. When it cools off a little here I will reshoot. Thanks very much for your help.
What is the cause, got same problem with 6.5 PRC . I have to raise velocity 75fps to match POA, don"t know what to trust, ballistic app or chrono
 

Straight Shooter

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Foul bore, as I said above, I had miscalculated my yardage. I was shooting from 285 yards instead of 300. The numbers are right on the button for shooting from 285 yards.
 

Tulsa Reiner

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Tulsa, OK
Zero is right on. MV is 2725 fps with a 140 hornaday BTHP with a BC of .580. Really has me scratching my head.
SS: that looks like a G7 BC. Did you enter it as a G1 in your ballistics calculator?
I admit
Mystery has been solved, duh. I was only shooting from 285 yards instead of the 300 that I thought . Numbers are right on the button.
Thanks for telling us. This has been another excellent discussion.
 

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