Ballisic calculator problems

[tisme]

When using Shooter or Strelock both give me very much the same corrections only both are out (high) from 200-400 and then fine from 500ish - 1000 yards.
I using a Magnetospeed to chrono, my BC is from Litz and I have tried others. I Zero at 100yards that is checked and also checked scope hight.
I must be doing something wrong or is it that the first few hundred yards the bullet is travelling faster and has a higher BC than the overall speed?

 

[brian427cobra]

Garbage in Garbage out, you mentioned 2 out of the three things, speed, BC, but what about atmosphrics, where are getting that info from?

 

[lpreddick]

sight height got me at long range. i used the hornady ballistic calculator and didn't enter my sight height. once corrected, my hits were spot on.

 

[Ledd Slinger]

When using Shooter or Strelock both give me very much the same corrections only both are out (high) from 200-400 and then fine from 500ish - 1000 yards.
I using a Magnetospeed to chrono, my BC is from Litz and I have tried others. I Zero at 100yards that is checked and also checked scope hight.
I must be doing something wrong or is it that the first few hundred yards the bullet is travelling faster and has a higher BC than the overall speed?

Problem is you are trusting a computer calculation too much. They only get you close. Doesn't make 2 cents worth of difference if your hits match up with the calculations or not. Whatever your rifle is actually doing is what counts. You have absolutely nothing to worry about if things don't match up.

 

[Lapua40X]

Problem is you are trusting a computer calculation too much....

Yep - don't let the computer calcs drive your dope sheet.
Run the initial dope sheet based on your theoretical data. Then shoot your targets and adjust your dope sheet to reflect real data.

 

[tisme]

sight height got me at long range. i used the hornady ballistic calculator and didn't enter my sight height. once corrected, my hits were spot on.

Thanks, sight height is bang on.

 

[tisme]

Garbage in Garbage out, you mentioned 2 out of the three things, speed, BC, but what about atmosphrics, where are getting that info from?

Don't think it's garbage in as it's right from 500 yards to 1000yards. I use a Kestrel 4000 for weather info.

 

[tisme]

Problem is you are trusting a computer calculation too much. They only get you close. Doesn't make 2 cents worth of difference if your hits match up with the calculations or not. Whatever your rifle is actually doing is what counts. You have absolutely nothing to worry about if things don't match up.

Trying to get first round hits so I would like to get it as close as possible. At 800yards I shot a 4" V bull but at 300 yards I was in the 2 ring.

 

[tisme]

Problem is you are trusting a computer calculation too much....

Yep - don't let the computer calcs drive your dope sheet.
Run the initial dope sheet based on your theoretical data. Then shoot your targets and adjust your dope sheet to reflect real data.

Yep I might have to make up a dope sheet However it would have been nice to get the ballistic calculations right or at least understand why they are out.

 

[Ledd Slinger]

Problem is you are trusting a computer calculation too much....

Yep - don't let the computer calcs drive your dope sheet.
Run the initial dope sheet based on your theoretical data. Then shoot your targets and adjust your dope sheet to reflect real data.

Yep I might have to make up a dope sheet However it would have been nice to get the ballistic calculations right or at least understand why they are out.

Cuz it's a computer trying to tell the future. That's why they're a little out. Kinda like the weather man.

 

[tisme]

Problem is you are trusting a computer calculation too much....

Yep - don't let the computer calcs drive your dope sheet.
Run the initial dope sheet based on your theoretical data. Then shoot your targets and adjust your dope sheet to reflect real data.

Yep I might have to make up a dope sheet However it would have been nice to get the ballistic calculations right or at least understand why they are out.

Cuz it's a computer trying to tell the future. That's why they're a little out. Kinda like the weather man.

The weather man is out sometimes. My calculator is out all the time at the same place! (but I have seen some weather men that are like this)

 

[Joe R]

Like Yogi Berra used to say: "In theory there is no difference between theory and practice. In practice there is."

 

[brian427cobra]

Garbage in Garbage out, you mentioned 2 out of the three things, speed, BC, but what about atmosphrics, where are getting that info from?

Don't think it's garbage in as it's right from 500 yards to 1000yards. I use a Kestrel 4000 for weather info.

Ok so you know your speed, know your BC(or its very close) and you know what the weather is where your shooting, remeasure scope height, and try a different scope, I have most of the Ballistic programs on my iPhone but I pretty much only use my Kestrel 4500 with Apllidied Ballistic, I like that I can true the calculator to match my real world data

 

[Forum Boss]

Remember this: BC is dynamic. BC on bullets is not constant over the entire trajectory, as it can vary with speed and other factors. You can only enter one BC into most programs.

Hence it is not at all unusual for a bullet to be high at one point in trajectory and low at another point, when compared to ballistics program predictions.

 

[Steve Blair]

Are you using G1 or G7 B.C.?

 

[tisme]

Tried both G1 and G7.

Boss that was my thoughts as well. This would not explain why my calculator is in at longer distances though, as an average BC would make the calculations right at an average distance. Or would it? It might make it right at 3/4 distance (750 yards ish)

Dose anyone on this forum make a ballistic calculator and how hard would it be to input different BCs at different speeds?
Why aren't the calculators programmed to cope with this? The BCs for speed is published by bullet manufacturers like Sierra.

 

[dragman]

Just my opinion,
You don't know your BC after the bullet is fired, it is going to change if ever so slightly. So to correct this I make sure everything is as close as I can get it and verify that my 100 yard Zero is right on then take it out long 1050-1250 yards somewhere in there and check it. then I adjust my fps on my chart to match what I just verified. I also run charts for every 10 degrees of temp because out LONG I don't care how stable your load or powder is it's going to change a couple clicks and that can be the difference between a hit or miss on a ground hog.
There is lots more to consider with shooting out long but this is the basics that I use.

 

[Terry_M]

I believe that the G7 ballistic calculator does allow for different BC's and allows you to input the manufacturers information for BC per FPS and calculates that in for you at a specific distance.

 

[FeMan]

As stated, the actual BC varies with speed. Some manufacturers list their highest and some the average; some list calculated and some measured.

For whatever reason, even when using Brian Litz measured BC values, I have to drop them by between 5% and 7% to mimic actual trajectories. Once I do that everything comes into line as long as all my other inputs are accurate.

 

[Laurie]

Remember this: BC is dynamic. BC on bullets is not constant over the entire trajectory, as it can vary with speed and other factors. You can only enter one BC into most programs.

Hence it is not at all unusual for a bullet to be high at one point in trajectory and low at another point, when compared to ballistics program predictions.

Absolutely!

It's an average based on readings taken over the best part of 1,000 yards. Even though the G7 drag coefficient varies by velocity far less than that based on the G1 model, it still changes a bit. Then the G7 'reference projectile' and your bullet are unlikely to be identical - Bryan Litz chose it as the closest off the shelf model to a typical modern HPBT bullet.

You don't say how you're measuring real life against the ballistics program model. Come-ups in MOA from a zero? Have you checked your scope elevation adjuster accuracy on what actually happens at exactly 100 yards as opposed to what is expected to happen? ie 25-MOA on the scope turret = 25*1.047"=26.2" on the paper? How big is your group size in such an exercise? Measuring the distance between centres of two half-inch groups immediately throws a possible 2-3% variation into the mix. Is your zero distance precisely 100 yards (or whatever) to within an inch or two? Is the target also precisely whatever distance is believed too? I can think of one well known UK range, famous worldwide, where the 1,000 yard firing mound is actually 984 yards from the targets, so one's calculations are immediately 'out' no matter how good the program and the data fed in. How accurate is the Magnetospeed? (Great device, but I wouldn't expect it to 100% precise and even a 1% error on 3,000 fps puts your average MV out by 30 fps.)

Have you checked and calibrated your Kestrel readings against those from a professional meterologist's kit? How do you know whether the same air temperature applies to all of the air that the bullet flies through on a 1,000 yard flight? What's the wind speed and angle working on the bullet at every section of its flight?

............. and so on and so forth! The point is that we're talking lots of small variables and potential inaccuracies. (Not so small for scope adjusters as until very recently, 3-5% variation from reading to true was regarded as good.) On some occasions, they cancel themselves out, on others they add up one way or the other enough to create an 'inaccuracy'.