Balistics App Truing??

[woogie_man]

Ok I am using Strelok Pro and have been for some time. Typically I have no issues and things are typically spot on with the program. But today I found something and haven't thought of this.

When you are truing your calculations is it better to true the balistic coefficient or the velocity? When using a chronograph I am getting an average of 930 fps with my 30 grain slugs. Looking at the tube of Javelin slugs it is showing a BC of 0.094 when calculated at 950fps. Luckily enough these are in the Strwlok Pro app so I am using those numbers.

Now when I zero at 50 yards and then move back to 100 yards and do my correction, I can choose velocity or BC. If I change the velocity it gives me a speed of 955fps, and if I choose the bc it gives me a bc of 0.151.

Dies it really matter which one you choose or not? And is there an advantage to choosing one over the other?

I am planning on shooting out to 200 yards when I get to my other range, and that should help me true up the numbers a bit more.

 

[Vana2]

Interesting stuff woogie_man. Sorry. No suggestions for your question.

I use Chairgun in a casual sort of way - mostly to get a starting point to for the best point-blank range before I start shooting to determine what it actually is. I play "what if" to see what the program says but don't use the numbers. I make DOPE cards for each rifle and go with that.

I'm curious about the ballistic apps but wonder if they are worth while considering the potential errors in data that we have them work with.

As a designer by trade (retired) I know that everything has tolerances, nothing is perfect. My equipment (gauges, chronographs, range finder) may not be 100% accurate and ballistics are temperature/humidity sensitive; BC numbers are suspect and I do wonder how well the algorithms in the ballistic apps work.

I'm still trying to decide if it's worth the effort to figure out the ballistic calculators or just set up a target and take a couple of shots to get the range.

Please post your findings.

Cheers and good luck!

 

[woogie_man]

I enjoy the calculators as they give a rough estimation of what "dhould" happen. You then have to verify everything to make sure it is correct. Once you get things verified with the rifle, through a dope card, then true up the app and make them match.

I can't tell you how many times I have been out shooting and either forgot my dope sheet/book in my truck or forgot my phone. So having a back up is ALEAYS needed.

We should never be reliant 100% on calculations. That is the joy of tuning and setting things up!

 

[dizzums]

for any given gun, projectile, day, or distances involved it always takes some 'proofing' for me, then i can see where its at and pick a random factor to make the app closer so i can read things reasonably for that session .. if that makes sense .. theres 'cosmic' factors involved i could literally spend all my time chasing to try to make apps more accurate, nah, i need 2 hashes holdover for that shot, done ..

 

[stovepipe]

Ok I am using Strelok Pro and have been for some time. Typically I have no issues and things are typically spot on with the program. But today I found something and haven't thought of this.

When you are truing your calculations is it better to true the balistic coefficient or the velocity? When using a chronograph I am getting an average of 930 fps with my 30 grain slugs. Looking at the tube of Javelin slugs it is showing a BC of 0.094 when calculated at 950fps. Luckily enough these are in the Strwlok Pro app so I am using those numbers.

Now when I zero at 50 yards and then move back to 100 yards and do my correction, I can choose velocity or BC. If I change the velocity it gives me a speed of 955fps, and if I choose the bc it gives me a bc of 0.151.

Dies it really matter which one you choose or not? And is there an advantage to choosing one over the other?

I am planning on shooting out to 200 yards when I get to my other range, and that should help me true up the numbers a bit more.

I saw a youtube vid by Keith Gibson (68 whiskey channel) where he talks about strelok pro. The interesting thing I got from that vid was that strelok pro will allow you to use multiple ballistic coefficients and Keith uses them. In his case he told strelok to use one bc for out to about 150 yards, then use a different bc from 150 yards to some other distance beyond that, and then a third bc for the rest of the way.

So if you have dope for lots of distances out to 200 yards and beyond, you might not find a muzzle velocity and bc that matches up with all of your dope. If you do find a muzzle velocity and bc that matches up perfectly with your dope out to some distance beyond 100 yards, then the velocity is probably correct and you will have to play with additional bc's to get strelok to agree with your dope at the longer distances.

I haven't done any of this myself so I don't have any real-world specific examples to show. I have strelok pro, but I don't use all the features.

stovepipe

 

[stovepipe]

I saw a youtube vid by Keith Gibson (68 whiskey channel) where he talks about strelok pro. The interesting thing I got from that vid was that strelok pro will allow you to use multiple ballistic coefficients and Keith uses them. In his case he told strelok to use one bc for out to about 150 yards, then use a different bc from 150 yards to some other distance beyond that, and then a third bc for the rest of the way.

So if you have dope for lots of distances out to 200 yards and beyond, you might not find a muzzle velocity and bc that matches up with all of your dope. If you do find a muzzle velocity and bc that matches up perfectly with your dope out to some distance beyond 100 yards, then the velocity is probably correct and you will have to play with additional bc's to get strelok to agree with your dope at the longer distances.

I haven't done any of this myself so I don't have any real-world specific examples to show. I have strelok pro, but I don't use all the features.

stovepipe

I just watched the video again. I have to correct myself here. The multi-bc mode of strelok doesn't switch to a new bc based on distance -- it switches to a new bc based on the projectile's speed. That makes sense because I know the bc of projectiles changes as they slow down. Fun stuff.

stovepipe

 

[woogie_man]

Post a link to the video. I will dig for it as well and watch that again.

 

[stovepipe]

Post a link to the video. I will dig for it as well and watch that again.

stovepipe

 

[woogie_man]

Have honestly never used that function in the app. So now it sounds like I am going to need to shoot over my chrono further. lol

 

[Ballisticboy]

As ranges and velocity changes get larger, you will increasingly encounter difficulties matching firings. There are basic fundamental problems with using trajectory models which rely on the use of BCs. The reference drag law will never match the shape of the actual drag curve of the projectile. Coupled with this, many of the available models do not have suitable drag laws in the first place for pellets or slugs. In addition, many users do not put in the correct atmospheric conditions when calculating a BC from measured speeds, or when subsequently using the trajectory models.

None of this makes a great deal of difference when ranges are 50 yards or so, but as ranges get longer, then problems can occur. Using multiple BC values is one way to try to match at certain points, but it is not solving the basic problems with the use of BCs, or the inbuilt inaccuracies of the point mass model used by just about all the available trajectory models.

This is why many years ago the large calibre weapons trajectory models changed to purpose drag laws and modified point mass models which need a lot more input data than is available for bullets, pellets or slugs, unless you can create it yourself.