Balistic Software accuracy question

[earl1704]

"IF" ballistic software can predictor a bullets path and impact what happens when the data I enter does not correspond with the bullets impact?

What I have run into is the ballistic software will say the bullet will impact 1.5 inches low at 200 yds. The impact is really 2.25 inches low at 200 yds. Is the data (temp. wind, bullet weight, ect.) in error (I have a Kestrel) or is the software only a predictor and not precise?

Why can I not change the data on bullet impact at say 200 yds. 300 yds and 400 yds to where the bullet really hits and have the ballistic software predict a more accurate impact at 500, or 600, yds.?

I have Sierra's and Point Mass Ballistic Software.

Am I looking at this properly?

 

[KRP]

Exbal has a function that does that, it assumes all other data entered to be correct though and changes the muzzle velocity to attempt the correction. It will let you enter multiple BCs to make corrections between predicted and actual data also. I haven't used the software you have so I don't know if they have similar functions. Assuming the programs use the correct math, it is a matter of SISO I think.

 

[BryanLitz]

Earl,
If you're seeing a problem between 100 and 200 yards, my first thoughts are:
1) Be sure you're entering the proper sight height. This is the distance from the scope centerline to bore centerline.
2) Make sure you confirm your 100 yard zero is actually zero and hasn't drifted.
3) Make sure you're shooting enough rounds to resolve the true center of your groups. 3 shots from a 1 MOA rifle isn't enough to resolve the true center of a group within 3/4" at 200 yards.
4) Have you confirmed (measured) that the targets are actually 100 and 200 yards away? An error of +/-10 or 15 yards can give you trouble when trying to use a program in this way.

None of the above is meant as a criticism of you, but they're the potential errors that come to mind with a mismatch over such short range. When you're only talking 200 yards, the software doesn't have much distance for normal uncertainties in atmospherics, muzzle velocity or BC to have a great effect. It's more likely a problem with your fundamental set-up.

If you share your inputs we might be able to pinpoint anything that looks 'fishy' and help you diagnose the problem.

There's no reason for a ballistics program to actually be off by 3/4" at 200 yards, but there are a number of reasons why it may seem that way.

-Bryan

 

[earl1704]

Thanks for the information I think you may have hit it on the head, I have always used the Sierra's programs "given" scope height of 1.6. I measured the width of the scope at 2.30 divided by half = 1.15 and added the distance from the center of the bore to bottom of scope to get .94 so .94 plus 1.15 = 2.09.

I am new at this and really appreciate the help I keep finding the little things make a big difference. I will shoot this weekend and see if this firms up the numbers.

P.S. are you the Bryan Litz of Applied Ballistics for Long Range Shooting? If so I love your book although I am trying to put it all together in my head. I find if I read a chapter over and over it will sink in. I'll be working on your "Getting Control of Sights" this weekend. I really liked "dont take anything for granted" my shooting range has a 100 yd. target but acording to my range finder (and everyone's else I tried) its really 106 yds. and 400 yds. is really 422 yds. If I read your book correctly it dosent matter as long as I use my range finder and my gun and loads. Anyway your book has lots of information beginners like myself never think about.

Thanks, Earl

 

[BryanLitz]

Earl,
Yep, that's me. Thanks for your interest in my book; I'm glad to hear you're able to get something useful from it.
It's not uncommon for ranges to not be set up exactly right on the numbers, and that can give you trouble when trying to compare 'actual' vs predicted trajectories (if you don't know about it). However in your case, I think the sight height input will turn out to have the biggest affect.
Take care,
-Bryan