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Help Needed....MV Validation Puzzle

 
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Old 07-17-2013, 08:17 AM
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Join Date: Apr 2012
Location: PA
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Help Needed....MV Validation Puzzle

In the past couple months I have been plinking with my .223 Remington. I first worked up an acceptably accurate load at 100 yds. I then found my MV using an average of many rounds shot through my chronograph. I then plugged that MV, along with enviormental conditions, into my ballistic program (BulletFlight iphone app). I used those outputs to verify my trajectory at 450 yds. I started here thinking that the effective range of the .223 Rem cartridge is limited. In my mind a 600 yd groundhog shot with this rifle would be a feat in itself. Keep in mind this rifle will only be used for groundhog hunting, shorter range coyote hunting, and steel plate plinking. My 450 yd varification was a success and the round proved to be quite accurate. So last night I put some steel out at 675 yds. This plate was a square foot in size. When taking my first round sighter shot I was amazed that it struck a full 5.7 MOA low. By my calculations thats about 40"! After a redial and one more sighter I was on target and grouping around 1 moa with no problem. I don't expect the rifle to do much better than that at that distance but I can't understand what caused my program to be that far off. I am also unsure of what to do to correct it. If I tweak my MV in the program to the 675 yd validation it will throw all shorter range outputs way off. Any thoughts or suggestion would be greatly appreciated!
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Old 07-17-2013, 08:57 AM
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Location: New Bern, NC
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Re: Help Needed....MV Validation Puzzle

I don't know of your program accounts for it, but double check your BC, alt, baro, humidity, and especially scope height. If this measurement is only slight off your longer range tragectory will greatly suffer. Are you shooting factory or hand loads?
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Old 07-17-2013, 10:03 AM
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Join Date: Apr 2012
Location: PA
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Re: Help Needed....MV Validation Puzzle

Quote:
Originally Posted by JARHEAD1371 View Post
I don't know of your program accounts for it, but double check your BC, alt, baro, humidity, and especially scope height. If this measurement is only slight off your longer range tragectory will greatly suffer. Are you shooting factory or hand loads?
Thanks for the input JARHEAD. I have accuratley accounted for MV, zero range, scope height, G1 BC, Range (to the yd), Temp., Baro Pres., Angle of Shot, and Altitude. One thing that I have done is entered a station pressure for my Baro. Pres. To my understadning, I should then enter 0 for my altitude. I may have misread this information which could be the cause. Am I understanding this correctly? The odd thing was that this happened for my friends 280 AI in the same manner on the same evening. His dial was dead on at 675 (which is very near the yardage I verified his MV at) and was later 10 MOA off at 1030yds. Once on target at 1030yds his rifle performed amazingly. So both rifles acted similarly with data entry as accurate as possible with my skill set. What is causing my program to be so dramatically off at longer distances. I have heard of using multiple BC's entered into a program and have the option to do so but am unsure of how multiple BC's work. In addition I don't know if that is the problem or if I am over looking something. Any other thoughts?
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Old 07-17-2013, 10:27 AM
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Join Date: Nov 2012
Location: Green River, Wyoming
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Re: Help Needed....MV Validation Puzzle

Quote:
Originally Posted by Hunter15 View Post
... I have heard of using multiple BC's entered into a program and have the option to do so but am unsure of how multiple BC's work....
Hunter,
If I may... (and there's many on here who understand this much better than I do...)

I seemed to have this problem with a friends 22-250. My calculations were good to 350 or 400 yds but at 600 or so the bullets were hitting quite a bit low. As a bullet flies downrange and decreases in veloctiy it also loses BC value. This is one reason that on Sierra's website they list multiple BCs for a given bullet, based on the veloctiy.

EX: A .224 cal 55gr Sierra BlitzKing has a BC of .271 @ 3100 fps and above. But they also list the following:
BC= .264 between 3100 and 2550 fps;
.250 between 2550 and 2050 fps;
.236 between 2050 and 1800 fps;
.224 @ 1800 fps and below
https://www.sierrabullets.com/store/...5-gr-BlitzKing

For my friend's 22-250 I had an original starting BC which was good from 0-400 yds and then a lower BC which was valid from 400-600 yds, etc...

Hope that made some sort of sense... maybe someone with more experience will chime in as well...

-Clint
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Last edited by CB11WYO; 07-17-2013 at 11:42 AM. Reason: wrong URL
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