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trajectory calculator help

 
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  #1  
Old 09-15-2012, 09:40 PM
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Join Date: Aug 2012
Posts: 13
trajectory calculator help

Help!
I'm having trouble getting that JBM simplified trajectory calculator to work for me. I'm attempting to duplicate my real world results with my 223. At 290 yards I dial 2.5 MOA from my 100 yard zero and am right on. The calculator says it should be 4 MOA! I just shot this again today for verification.
Here's what i'm shooting.
Bushy Predator 20", 2945fps, 60gr. V-Max over 25 gr. of Varget.
I'm shooting from a bench with my targets at my same elevation. My scope sits at 1.75" above the bor. 75 to 85 F at 550 ft. with about 65% humidity. I'm useing a Leupold 4-12 Mark AR with 1/2 moa clicks. I'm using the bullet library and imputing what I have listed here.
What am I doing wrong?
Thank for your hep.
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  #2  
Old 09-15-2012, 10:00 PM
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Join Date: Jan 2012
Location: Hot Springs, South Dakota
Posts: 504
Re: trajectory calculator help

What I see is that you will need to validate your real world trajectory and at least one more distance. Once you have done that, or even before, you will either have to change your velocity, or BC (usually velocity) in your ballistics program to math your real world trajectory.

In short word, validate.
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  #3  
Old 09-16-2012, 02:50 AM
Platinum Member
 
Join Date: Feb 2005
Location: Nevada
Posts: 2,782
Re: trajectory calculator help

4-4.2 MOA is about right... with 1/2 moa clicks you'd have to round down to 4.0 MOA and go 8 clicks up...

Now, make sure the center of 3 shotS group matches with the center of the target at
100 yards; then go 8 clicks up and still shoot at 100 yards, if the center of the group
is not between 4 and 4.6" high then it would give you a pretty good idea about how
the scope is tracking. If it prints where expected then shoot it at 300 yards and it should
be very close.

Do pay attention and take in account how small of a group the shooter/rifle combo are capable of.
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Our Lord Jesus said that as it was in the days of Noah and
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  #4  
Old 09-16-2012, 06:31 AM
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Join Date: Aug 2012
Posts: 13
Re: trajectory calculator help

Eaglet,
I have done that twice now. I'm only having to move up 5 clicks and at 100 yards it prints 2.4"high.
Correction: my scope height is 2.6" Not 1.75".
For the other yardage test I would think that farther is better than close, or would 200 work just as well as long as I'm very accurate with the measurements?
Just in case it matters, my 10 shot ES is 34 and SD is 11.
I always shoot a minimum of 5 shot groups.
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  #5  
Old 09-16-2012, 11:59 AM
Gold Member
 
Join Date: Jan 2012
Location: Hot Springs, South Dakota
Posts: 504
Re: trajectory calculator help

Quote:
Originally Posted by Round2it View Post
Eaglet,
I have done that twice now. I'm only having to move up 5 clicks and at 100 yards it prints 2.4"high.
Correction: my scope height is 2.6" Not 1.75".
For the other yardage test I would think that farther is better than close, or would 200 work just as well as long as I'm very accurate with the measurements?
Just in case it matters, my 10 shot ES is 34 and SD is 11.
I always shoot a minimum of 5 shot groups.
The further out you can do the validation the better. I try to do mine every 100 yards out to the distance that I feel comfortable shooting. The more accurate data, the more accurate your ballistic calculators will be.
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  #6  
Old 09-16-2012, 05:48 PM
Junior Member
 
Join Date: Aug 2012
Posts: 13
Re: trajectory calculator help

I will get that done next week see what results I get.
Thanks
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  #7  
Old 09-16-2012, 10:22 PM
Platinum Member
 
Join Date: Feb 2005
Location: Nevada
Posts: 2,782
Re: trajectory calculator help

Quote:
Originally Posted by Round2it View Post
Eaglet,
I have done that twice now. I'm only having to move up 5 clicks and at 100 yards it prints 2.4"high.
Correction: my scope height is 2.6" Not 1.75".
For the other yardage test I would think that farther is better than close, or would 200 work just as well as long as I'm very accurate with the measurements?
Just in case it matters, my 10 shot ES is 34 and SD is 11.
I always shoot a minimum of 5 shot groups.
Alright, I used JBM and punched in all info. 29.9 for pressure, 2.6" for scope height
and to 290 yards, it calculates 3.4 MOA of adjustment needed. That would put us at
7 clicks. U're already using 5 clicks so for that distance one full MOA is too much of a difference...

I think that factory ammo in that bullet weight has a muzzle velocity of about 3150 ft/sec
...thinking aloud here.. If you were to have a muzzle velocity of 3250 ft/sec then you
would only need 5 clicks up to be dead on @ 290 yards... Can that be possible?
__________________
-----------------------------

-----------------------------
HEBREWS 13:8
Jesus Christ the same yesterday, and to day, and for ever.

Our Lord Jesus said that as it was in the days of Noah and
also as it was in the days of Lot so it shall be in the days...
It's happening again!!! God sent to us His prophet, and His Word
to this generation and we once more are rejecting it as was prophesied!!!

---> As promised, God Sent His Prophet to us!
Reply With Quote
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