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HELP Ballistics program wrong

 
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  #1  
Old 11-13-2010, 11:52 PM
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HELP Ballistics program wrong

hey Im brand new to the site. I shoot a tikka T3 HB stainless varmint. chambered in 204 ruger. I hand load with as much accuracy as i can. I have a 6-24 x 50 bushnell 4200 tactical scope. zeroed at 300yds. shooting a 32 gr vmax with 28 grains of h4895. I chronyed my loads and entered all my info in to 3 different programs. they all basically said to dial my turret up 13.2- 13.7 MOA. so I did and was shooting at 700yds( GPS verified) and after a bunch of missing and moving closer to the target 500yds. I had to turn my scope up to 16.75 MOA to hit the paper at 700yds. my first group was 9 inches. why is the ballistics program not even close?

any help of ideas would be greatly appreciated

Thanks
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  #2  
Old 11-14-2010, 02:08 AM
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Location: NW Mt.
Posts: 600
Re: HELP Ballistics program wrong

Have you ever shot a box with your scope to check it's accuracy?
Have you ever checked your chrono against another?
Did you enter the baro, humidity and temp correctly?
Are you dead sure of the wind speed over the entire 700 yards?
Did you check the bc of the bullet out to 300 or 400 yards and
then see what the change was in bc vs. fps over the 700 yard distance?

Shooting such a light bullet over that great a distance is a real challenge,
everything matters.
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  #3  
Old 11-15-2010, 01:42 AM
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Join Date: Nov 2010
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Re: HELP Ballistics program wrong

By shooting a box what do yo mean?

How do i measure or check BC. I am very new to this long range stuff.

will wind play into the vertical drop of a bullet or just the horizontal?

I think my scope is accurate. I was shooting at 420yds the same day 5 shot group was 2.25in.

Ya i entered everything as close as i could I dont have a weather station.

I Haven't checked my chrony but the data I was getting was very close to the load recipe data
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  #4  
Old 11-15-2010, 08:50 AM
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Location: SW Montana
Posts: 4,549
Re: HELP Ballistics program wrong

Ballistics programs are just calculators, junk in junk out kinda things. The first steps to having accurate corrections is to know how you scope adjusts, they can be all over the map, few move in actual MOA. I lock my gun in a vice and at a measured hundred yards turn the turret through the full range while watching a surveying stick to check what I'm turning so I can give the program the actual value my optic adjusts in.
Then I take a tall piece of card board on a wood frame and us one aim point at the top then walk it out every 100yrds and shoot a group with the same aim point, this will give you your actual bullet drop, then I re shoot all that but dial the drop value I have measured from actual shooting to verify that everything is GTG! Then you know what your rifle and scope actually do so that you can take that to a ballistics program and tweak it to get on target, I tweak the BC's little under a 1000yrds but a change in velocity will usually get you on once you've verified you rig. Crony's can be a week link in the process.
How you deal with the weather data is very important and can really though you of, make sure you use deal with barometric pressure correctly, I think there is a sticky that deals with this in one of the forums. Don't add an elevation with station pressure is the basic idea.
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Last edited by bigngreen; 11-15-2010 at 08:54 AM.
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  #5  
Old 11-15-2010, 08:56 AM
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Join Date: Nov 2007
Posts: 78
Re: HELP Ballistics program wrong

I am not intimately familiar with the .204 and its bullets, however in general such a light bullet will likely be losing velocity very quickly at those ranges,which means that any inaccuracy in the data input can cause a very large difference between actual impact and predicted. You are likely at the extreme edge past 500 or so. Not that you cant do it, its just going to require excellent preparation.

Different software can be more or less accurate, but I am going to guess that the compounding errors in data are the problem and not the software. For giggles enter some values around the values you entered. I suspect you will find that a small atmosphere difference can account for your error way out there.

Listed in a very lose order of importance are factors you should consider, assuming that you have verified the click values of the scope and mechanicals of the gun.

Atmospheric pressure and temperature

Angle of sight for the shot,

actual BC of the bullet at different speeds

accurate range estimation... GPS may not be good enough for your combo. Plus or minus 10 yds on each data point could do it.

at that range, the error in the chronograph speed could also account for the error you report.

Many other small factors i have likely forgotten to list.
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  #6  
Old 11-17-2010, 05:57 PM
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Join Date: Nov 2010
Posts: 3
Re: HELP Ballistics program wrong

Thanks for the great input guys... You defiantly gave me a bunch of stuff to think about and consider. I'll have to get out sometime here and do the long paper/shoot every 100yds to get an exact picture of my cartridge.
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  #7  
Old 11-17-2010, 08:29 PM
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Location: Wilmington NC
Posts: 4,222
Re: HELP Ballistics program wrong

My bet is that your scope clicks are not at true .25 MOA and that is the difference.

How do you know your chrono is accurate? Have you checked against anothe one?

BH
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