I've read up a lot on how to tweak ballistic calculators to get them to match your actual dope and the 1st place to start changing numbers appears to be the BC. Why is that? It seems that with the work that Brian Litz and others have done to get accurate BCs, it occurs to me the BC (Litz's G7 anyway) would be fairly accurate and instead MV, scope height or some other variable would be the areas to tweak. So why is BC usually the 1st place most people play with to get dope to match?
Range Report Tweaking ballistic calculators
- Thread starter Notso
- Start date
Re: Tweaking ballistic calculators
Tweak the BC? For real?
Nah man I would not touch the BC.
Things to check
- Is your muzzle velocity correct?
- Are the atmospheric inputs in the calculator correct?
- Is the range correct?
- Is the rifle set up correctly in the calculator?
Disregarding wind, if all of those inputs are correct, and the MV remains constant you should get excellent dope out of a ballistics calc.
If your wind reading skills are up to scratch and the wind is constant value for the entire flight of the bullet then by all means use the calculators windage adjustments... but this will rarely be the case
Tweak the BC? For real?
Nah man I would not touch the BC.
Things to check
- Is your muzzle velocity correct?
- Are the atmospheric inputs in the calculator correct?
- Is the range correct?
- Is the rifle set up correctly in the calculator?
Disregarding wind, if all of those inputs are correct, and the MV remains constant you should get excellent dope out of a ballistics calc.
If your wind reading skills are up to scratch and the wind is constant value for the entire flight of the bullet then by all means use the calculators windage adjustments... but this will rarely be the case
Re: Tweaking ballistic calculators
If I have a Brian Litz BC, I tweak the muzzle velocity, so that the output of the ballistic program matches my shooting data at the longest range where I'm sure the bullet is still supersonic.
You may find this interesting reading: Sources of Ballistic Program Inaccuracies
If I have a Brian Litz BC, I tweak the muzzle velocity, so that the output of the ballistic program matches my shooting data at the longest range where I'm sure the bullet is still supersonic.
You may find this interesting reading: Sources of Ballistic Program Inaccuracies
Re: Tweaking ballistic calculators
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vman</div><div class="ubbcode-body">Things to check
- Is your muzzle velocity correct?
- Are the atmospheric inputs in the calculator correct?
- Is the range correct?
- Is the rifle set up correctly in the calculator?</div></div>
+1
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vman</div><div class="ubbcode-body">Things to check
- Is your muzzle velocity correct?
- Are the atmospheric inputs in the calculator correct?
- Is the range correct?
- Is the rifle set up correctly in the calculator?</div></div>
+1
Re: Tweaking ballistic calculators
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">If I have a Brian Litz BC, I tweak the muzzle velocity, so that the output of the ballistic program matches my shooting data at the longest range where I'm sure the bullet is still supersonic.
You may find this interesting reading: Sources of Ballistic Program Inaccuracies
</div></div>
Yep, I've read that before and I understand the GIGO principle and where the sources of inaccuracy lay. I was simply asking why so many others seem to recommend tweaking the BC 1st to get your dope to match your ballistic output. Seemed counter-intuitive to me and I personaly DON'T mess with the BC - but I thought there might be a reason I wasn't aware of.
FTR - I personally tend to tweak MV before anything else because I think unless you have a commercial grade chrono - even the best chrono is not going to be perfect. Especially since there is no such thing as "calibrating" them once they leave the factory. In fact, I'm not sure how or if they're even calibrated at all. For the other stuff, I use a Kestral for temp, RH and station pressure and its served me very well using the Bulletflight app. I can get my dope to be VERY close to the ballistic output (or vice versa) - but I've been a .1 or .2 mil off from actual dope at times and would like to tweak the program to be dead on with my dope. I trust the bullet before I do the computer.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">If I have a Brian Litz BC, I tweak the muzzle velocity, so that the output of the ballistic program matches my shooting data at the longest range where I'm sure the bullet is still supersonic.
You may find this interesting reading: Sources of Ballistic Program Inaccuracies
</div></div>
Yep, I've read that before and I understand the GIGO principle and where the sources of inaccuracy lay. I was simply asking why so many others seem to recommend tweaking the BC 1st to get your dope to match your ballistic output. Seemed counter-intuitive to me and I personaly DON'T mess with the BC - but I thought there might be a reason I wasn't aware of.
FTR - I personally tend to tweak MV before anything else because I think unless you have a commercial grade chrono - even the best chrono is not going to be perfect. Especially since there is no such thing as "calibrating" them once they leave the factory. In fact, I'm not sure how or if they're even calibrated at all. For the other stuff, I use a Kestral for temp, RH and station pressure and its served me very well using the Bulletflight app. I can get my dope to be VERY close to the ballistic output (or vice versa) - but I've been a .1 or .2 mil off from actual dope at times and would like to tweak the program to be dead on with my dope. I trust the bullet before I do the computer.
Re: Tweaking ballistic calculators
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Notso</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">If I have a Brian Litz BC, I tweak the muzzle velocity, so that the output of the ballistic program matches my shooting data at the longest range where I'm sure the bullet is still supersonic.
You may find this interesting reading: Sources of Ballistic Program Inaccuracies
</div></div>
Yep, I've read that before and I understand the GIGO principle and where the sources of inaccuracy lay. I was simply asking why so many others seem to recommend tweaking the BC 1st to get your dope to match your ballistic output. Seemed counter-intuitive to me and I personaly DON'T mess with the BC - but I thought there might be a reason I wasn't aware of.
FTR - I personally tend to tweak MV before anything else because I think unless you have a commercial grade chrono - even the best chrono is not going to be perfect. Especially since there is no such thing as "calibrating" them once they leave the factory. In fact, I'm not sure how or if they're even calibrated at all. For the other stuff, I use a Kestral for temp, RH and station pressure and its served me very well using the Bulletflight app. I can get my dope to be VERY close to the ballistic output (or vice versa) - but I've been a .1 or .2 mil off from actual dope at times and would like to tweak the program to be dead on with my dope. I trust the bullet before I do the computer. </div></div>
You will probably NEVER be able to get your dope to be the exact same Every Day, as what the ballistic program states. Especially due to the reasons you stated, temp, RH and station pressure, etc. Way too many variables, just let it go. Being only .1mil off at one or two ranges is not that big o' deal. Hell, jerkin the trigger will screw up your dope more than that will.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Notso</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">If I have a Brian Litz BC, I tweak the muzzle velocity, so that the output of the ballistic program matches my shooting data at the longest range where I'm sure the bullet is still supersonic.
You may find this interesting reading: Sources of Ballistic Program Inaccuracies
</div></div>
Yep, I've read that before and I understand the GIGO principle and where the sources of inaccuracy lay. I was simply asking why so many others seem to recommend tweaking the BC 1st to get your dope to match your ballistic output. Seemed counter-intuitive to me and I personaly DON'T mess with the BC - but I thought there might be a reason I wasn't aware of.
FTR - I personally tend to tweak MV before anything else because I think unless you have a commercial grade chrono - even the best chrono is not going to be perfect. Especially since there is no such thing as "calibrating" them once they leave the factory. In fact, I'm not sure how or if they're even calibrated at all. For the other stuff, I use a Kestral for temp, RH and station pressure and its served me very well using the Bulletflight app. I can get my dope to be VERY close to the ballistic output (or vice versa) - but I've been a .1 or .2 mil off from actual dope at times and would like to tweak the program to be dead on with my dope. I trust the bullet before I do the computer. </div></div>
You will probably NEVER be able to get your dope to be the exact same Every Day, as what the ballistic program states. Especially due to the reasons you stated, temp, RH and station pressure, etc. Way too many variables, just let it go. Being only .1mil off at one or two ranges is not that big o' deal. Hell, jerkin the trigger will screw up your dope more than that will.
Re: Tweaking ballistic calculators
Lindy,
I am working with the Field Firing Solutions program and it is asking for a lot of data that will calculate an accurate BC. Is BC determined by the bullet alone or is it a combination of speed, twist and bullet? Does each rifle, load combination have its own specific BC?
Lindy,
I am working with the Field Firing Solutions program and it is asking for a lot of data that will calculate an accurate BC. Is BC determined by the bullet alone or is it a combination of speed, twist and bullet? Does each rifle, load combination have its own specific BC?
Re: Tweaking ballistic calculators
The point of that process is make the program output match your field shooting data as closely as possible.
FFS uses only G1 BCs. I run FFS using a Bryan Litz corrected G1 BC for the bullet I'm shooting, and then I tweak the DK to get the program to match my field data.
I don't worry about that tool to calculate a BC.
The point of that process is make the program output match your field shooting data as closely as possible.
FFS uses only G1 BCs. I run FFS using a Bryan Litz corrected G1 BC for the bullet I'm shooting, and then I tweak the DK to get the program to match my field data.
I don't worry about that tool to calculate a BC.
Re: Tweaking ballistic calculators
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Swan</div><div class="ubbcode-body">
You will probably NEVER be able to get your dope to be the exact same Every Day, as what the ballistic program states. Especially due to the reasons you stated, temp, RH and station pressure, etc. Way too many variables, just let it go. Being only .1mil off at one or two ranges is not that big o' deal. Hell, jerkin the trigger will screw up your dope more than that will. </div></div>
Swan, I completely agree with you. I'm happy with being within a couple tenths of the predicted numbers. I was just trying to figure out why numerous people seemed to say tweak the BC 1st. It made no sense. Based on the responses so far, to the contrary, I'm beginning to think they (previous folks i was referring to) were pulling it out of their ass.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Swan</div><div class="ubbcode-body">
You will probably NEVER be able to get your dope to be the exact same Every Day, as what the ballistic program states. Especially due to the reasons you stated, temp, RH and station pressure, etc. Way too many variables, just let it go. Being only .1mil off at one or two ranges is not that big o' deal. Hell, jerkin the trigger will screw up your dope more than that will. </div></div>
Swan, I completely agree with you. I'm happy with being within a couple tenths of the predicted numbers. I was just trying to figure out why numerous people seemed to say tweak the BC 1st. It made no sense. Based on the responses so far, to the contrary, I'm beginning to think they (previous folks i was referring to) were pulling it out of their ass.
Re: Tweaking ballistic calculators
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">...pulling it out of their ass.</div></div>
No, they weren't.
Manufacturer-supplied BCs have tended to be optimistic, so that's what people would tweak first, especially if they have a chronograph in which they have a fair degree of confidence.
Now, however, with Bryan Litz's excellent work on actually testing bullets as well as supplying tested G7 BCs, you should probably tweak the muzzle velocity first <span style="font-style: italic">if you are using Bryan's BCs.</span>
But, for the reasons I listed in the link I posted, you're probably going to have to tweak <span style="font-style: italic">something</span>. BC is not a bad choice, especially if you're shooting a bullet which Bryan doesn't have a BC for.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">...pulling it out of their ass.</div></div>
No, they weren't.
Manufacturer-supplied BCs have tended to be optimistic, so that's what people would tweak first, especially if they have a chronograph in which they have a fair degree of confidence.
Now, however, with Bryan Litz's excellent work on actually testing bullets as well as supplying tested G7 BCs, you should probably tweak the muzzle velocity first <span style="font-style: italic">if you are using Bryan's BCs.</span>
But, for the reasons I listed in the link I posted, you're probably going to have to tweak <span style="font-style: italic">something</span>. BC is not a bad choice, especially if you're shooting a bullet which Bryan doesn't have a BC for.
Re: Tweaking ballistic calculators
Good advice. With a .308, the danger space on a 12" target at 1000 yards is only about 8 yards.
Good advice. With a .308, the danger space on a 12" target at 1000 yards is only about 8 yards.
Re: Tweaking ballistic calculators
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">...pulling it out of their ass.</div></div>
No, they weren't.
Manufacturer-supplied BCs have tended to be optimistic, so that's what people would tweak first, especially if they have a chronograph in which they have a fair degree of confidence.
Now, however, with Bryan Litz's excellent work on actually testing bullets as well as supplying tested G7 BCs, you should probably tweak the muzzle velocity first <span style="font-style: italic">if you are using Bryan's BCs.</span>
But, for the reasons I listed in the link I posted, you're probably going to have to tweak <span style="font-style: italic">something</span>. BC is not a bad choice, especially if you're shooting a bullet which Bryan doesn't have a BC for.
</div></div>
OK, that makes more sense now. I can understand tweaking the OEM G1 BCs. I only use Litz G7s, so I tweak MV 1st and it seems to get me very close. Thanks Lindy!
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">...pulling it out of their ass.</div></div>
No, they weren't.
Manufacturer-supplied BCs have tended to be optimistic, so that's what people would tweak first, especially if they have a chronograph in which they have a fair degree of confidence.
Now, however, with Bryan Litz's excellent work on actually testing bullets as well as supplying tested G7 BCs, you should probably tweak the muzzle velocity first <span style="font-style: italic">if you are using Bryan's BCs.</span>
But, for the reasons I listed in the link I posted, you're probably going to have to tweak <span style="font-style: italic">something</span>. BC is not a bad choice, especially if you're shooting a bullet which Bryan doesn't have a BC for.
</div></div>
OK, that makes more sense now. I can understand tweaking the OEM G1 BCs. I only use Litz G7s, so I tweak MV 1st and it seems to get me very close. Thanks Lindy!
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