Ballistic Calc vs. Actual, question in here somewhere...

[338 dude]

Hmm, I'm sure I got .611 BC for my velocity range off the Sierra website. So there's one thing I can correct.

As mentioned in the post above this page is for your bullet from Bryan Litz his book the ballistic performance of rifle bullets third edition

 

[wedgy]

Are you using G1 or G7 for BC ? I thing Sierra list in G1 but I would suggest G7 as it is more accurate past ~500 yards. G1 is for flat based roundish nose bullets while G7 is for boat tail VLD style.
Plug you #'s in Berger's calculator and see what you get(in MOA);
https://www.bergerbullets.com/ballistics/php/bb.php

 

[AccelR8]

Actually rocket science IS ballistics.

Past 600 yards BC values will have a big effect on the accuracy of your ballistics calculator and most manufacturers don't provide very accurate BC values, but Sierra at least breaks their BC values down in to velocity ranges (0 to 2000 FPS, 2000 to 2800 FPS, a 2800 FPS and above). At a minimum you need to use a ballistics calculator that accepts multiple BC values and use them. Bryan Litz's book Ballistic Performance of Rifle bullets 3rd edition, lists quite a number of bullets and their BC values that he developed using radar. He breaks the BC values down in to different ranges than Sierra (0 to 1500 FPS, 1500 to 2000 FPS, 2000 to 2500 FPS, 2500 to 3000 FPS, and above 3000 FPS) and he lists both the G1 and G7 BC values.

I don't know which bullet you're using but if you take a 140gr Sierra Matchking as an example and compare the 1000 yard drop using Sierra's BC values and Bryan Litz's G7 BC values you see a difference of 4.5 inches of drop. That's assuming that you used all the BC values and not just an average. If you used the average G1 value vs. the average G7 value there is a 5 inch difference at 1000 yards. With your exact bullet there may be more or less of a difference but there will be a difference.

This something I've wondered about ballistics calculators in general. Are they capable of accounting for BC changes related to velocity degradation. You seem to be saying they cannot unless you tell them too. Good to know.

edit; removed something I figured out on my own

 

[338 dude]

This something I've wondered about ballistics calculators in general. Are they capable of accounting for BC changes related to velocity degradation. You seem to be saying they cannot unless you tell them too. Good to know.

I use the Shooter app and run multiple bc’s straight out of Bryan’s book and everything works out extremely well for me very little trajectory validation adjustments

 

[Lone Hunter]

Quick look at JBM. Don’t have your sight height plus other variables but you can see how it works. You need proper data to get good outputs

 

[rammac]

I use Litz's G7 values and have very little truing/validation adjustment for my shooting, I use a .308 Win so my drops are pretty big and any ballistics engine errors show up pretty quickly.

 

[338 dude]

This something I've wondered about ballistics calculators in general. Are they capable of accounting for BC changes related to velocity degradation. You seem to be saying they cannot unless you tell them too. Good to know.

When I first got Strelok it was set on Multi BC. I switched it to G1. I can't find how to set it back to multi. I can change to G7 and a list of others but Multi is not there...?

I use an iPhone there are certain settings in the settings menu of your phone then scroll down to your ballistics application

 

[AccelR8]

I use an iPhone there are certain settings in the settings menu of your phone then scroll down to your ballistics application

Thanks. I figured it out. Basically I was mistaken...

 

[AccelR8]

I've used several different on line ballistic calculators and they all return results very similar to Strelok

 

[AccelR8]

As mentioned in the post above this page is for your bullet from Bryan Litz his book the ballistic performance of rifle bullets third edition

Yes I knew that. Thanks for posting that, that is good information I didn't have access to.

 

[AccelR8]

Are you using G1 or G7 for BC ? I thing Sierra list in G1 but I would suggest G7 as it is more accurate past ~500 yards. G1 is for flat based roundish nose bullets while G7 is for boat tail VLD style.
Plug you #'s in Berger's calculator and see what you get(in MOA);
https://www.bergerbullets.com/ballistics/php/bb.php

Using G7. Actually it seems that using either one only results in small changes for example at 1000, 308" vs 311" drop. But I use G7.

 

[338 dude]

Yes I knew that. Thanks for posting that, that is good information I didn't have access to.

I will gladly look up any bullet listed for anyone all you have to do is ask

 

[AccelR8]

First of all for ballistics no one talks or thinks in inches, you need to think in either moa or mils which are angular measures. If shots are all high out to 600yd then it is most likely the 1000yd is actually further. As mentioned you can use the good known dope out to 600yd to true the velocity using Strelok, then make a range chart to compare your "1000" results to find out the actual distance. But how did you determine 114" low, that's an extremely large target.

I determined 114” because after I got dialed in on the center of the plate I had 40.5 minutes on my elevation dial when Strelok called for 29.6. 40.5 minus 29.6 equals 10.9.

10.9 multiplied by 10.47 inches (which is one MOA at 1000 yards) equals 114 1/8 inches.

 

[cheek9075]

Interesting, if I do my TV at 600 with my 11 MOA actual, I get Strelok gives me a MV of 2,767.

You got data input somewhere incorrect. beyond 600 everything comes into play. Check and recheck.

 

[Monte F]

Maybe it is at 1000 meters?

 

[AccelR8]

Well, I switched to G7 rather than G1, switched to multi BC and entered data from the Lintz book which 338 dude provided.

I take my 11 minutes which I dialed up to hit center at 600 yards and use the trajectory validation in Strelok, it returns a calculated velocity of 2,896 (not 2,767 I got with G1 and .611 BC and I also found one error I made somehow I had entered 12.5 MOA instead of 11 for trajectory validation ). 2,896 to me seems too high. But if I plug this into Berger's on line calc, my 40.5 minutes correlates with 1,245 yards.

So maybe I was actually shooting beyond 1,000. That's the simplest answer. However all indications are the range is in fact 1,000.

As I said earlier, at this point I am going to consider all of my data as suspect and go through and shoot it all again in order to validate. Also, I'll get Labradar data and see if I need to replace my Magnetospeed data.

Thanks for all the help. I'll let you all know how it turns out. Might be a little while though.

 

[ppaul]

Is there some reason that your scope is not suspect? At least take another one with you to try if you don't figure it out. Do you have access to a scope checker?

 

[kelbro]

Once you have established your dope at each range, what is it that you are wanting the app to do for you?

 

[Ggmac]

A little background info first:

The rifle is a 6.5 Creedmoor. I have previously only shot it as far as 500 yards. At that time it had a target scope on it and I was using a ballistic calculator app on my phone. The drops at various yardages were pretty near spot on.

I began having trouble with that calculator so I switched to another calculator. I also switched to a different scope because I wanted to get away from the 1/8 moa dot and fine cross hair of the target scope. I wanted a reticle with MOA sub-tensions.

Fast forward to now. I took the rifle out to 1,000 yards. In fact this is the first time I've ever shot anything beyond 600. First I did a tall-target test. The scope tracked vertically just fine and the math said the clicks were almost exactly ¼ MOA, with a .2% error (two-tenths of one percent). I zeroed the rifle at 100 yards.

Rather than try to talk MOA or number of clicks I guess the most concise way is to talk inches. I will describe my actual point of impact relative to the point of impact predicted by the calculator. So, at 200 yards my impact was 1 inch high. At 300 it was 3” high, at 400 5” high, 500 8” high and at 600, 9” high.

These results don't worry me much as in my opinion the differences are not that great. I can say it's due to a bunch of little errors stacking up, errors in actual velocity, actual distance, actual BC, weather and so on. No big deal.

But what has me scratching my head is this; when I moved to 1,000 yards my actual impact was 114 inches LOWER than predicted. At all other distances I was high and then going from 600 to 1,000 it flip-flopped and now I'm low, and by a substantial amount.

I've been racking my brain over this. I have checked and double checked my notes, and thinking did I make an error in counting my scope clicks? I've pretty much eliminated that as a possible explanation, and also my first shots at 1,000 after I dialed up to the predicted MOA and number of clicks, my first shots hit the ground well on front of the post holding the steel target. Easily 8 or 9 feet low.

In case you're thinking I was at the top of my scope travel and was topped out, no that wasn't it. I still had lots of “up” remaining and had no trouble dialing up more to get my hits centered on the target with “up” to spare.

So I guess my question is, um, WTF? Is this normal?

I know this is vague, but bare with me . Theres a few good articles in a Precision shooting book . Ill find it if interested. Its about the issue you’re having , but is very easily proved . The action , Rifle is a SMLE , British Lee enfield . At six hundred , less or same elevation as at 1000 . Now its been a long time since i read it and my numbers may be off , but it has to do with the actions flex . Its a very detailed read and im not doing justice to it by this . Pm me if you want more specifics on the article .

 

[CharlieNC]

Strelok Pro has a built in bullet library from which you can automatically download the bullet specs for either G1 or G7, but at 1000yd it doesn't matter at all. 11moa for 600yd sounds very low compared to my experience, and as you noted gave an unbelievably high velocity vs the measured 27xx which makes sense. All of the distances you're using sound suspect.