7mm CUSTOM BULLET MAKERS
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Bryan Litz Ballistics
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NeilNE,
I've got some updated BC data for your list. First of all, Berger changed the advertised BC of their 180 VLD from .698 to .684 a couple years ago.
I've developed a repeatable procedure for test firing bullets to determine ballistic coefficient. If you get Precision Shooting Magazine, the March issue has one of my articles about test firing the Berger .30 cal 155 grain VLD. Long story short, my test procedure uses acoustic sensors in 200 yard increments to measure time of flight out to 600 or 1000 yards. My BC measurements are repeatable to within +/- 2%, usually within +/- 1%.
Your list caught my eye because it has several of the 7mm bullets that I've tested. Of particular interest are the Berger and JLK 180 grain bullets. If you look at these bullets side by side, it's hard to tell a difference between them. I believe the JLK bullet dies were made from the same set of prints as the Berger VLD,Design by Bill Davis of Tioga Engineering). So this begs the question, why would these bullets have different BC's? They're the same weight and the same shape. This is just the kind of smoke and mirrors that makes shooters think there is something mysterious about BC's and exterior ballistics that's beyond the realm of human understanding. I was pleased with the results of my testing of these two bullets: the BC is the same, as expected. All is right with the world.
Part of the reason there is so much 'slop' in advertised BC's is because they're referenced to the G1 standard which is very speed sensitive. The G7 standard is more appropriate for long range bullets. Here are the results of my testing for these two bullets:
G1 BC's, averaged between 1500 fps and 3000 fps:
Berger 180 VLD: 0.659 lb/in^2
JLK 180: 0.645 lb/in^2
The reason the BC for the JLK is less is mostly because the meplat was significantly larger on the particular lot that I tested,0.075" vs 0.059"; see attached drawing).
For bullets like these, it's much better to use the G7 standard. The following BC's are referenced to the G7 standard, and are constant for all speeds.
G7 BC's:
Berger 180 VLD: 0.337 lb/in^2
JLK 180: 0.330 lb/in^2
Many modern ballistics programs, including the free online JBM ballistics programs are able to use BC's referenced to G7 standards. When available, these BC's are more appropriate for long range bullets.
Take care,
-Bryan
I've got some updated BC data for your list. First of all, Berger changed the advertised BC of their 180 VLD from .698 to .684 a couple years ago.
I've developed a repeatable procedure for test firing bullets to determine ballistic coefficient. If you get Precision Shooting Magazine, the March issue has one of my articles about test firing the Berger .30 cal 155 grain VLD. Long story short, my test procedure uses acoustic sensors in 200 yard increments to measure time of flight out to 600 or 1000 yards. My BC measurements are repeatable to within +/- 2%, usually within +/- 1%.
Your list caught my eye because it has several of the 7mm bullets that I've tested. Of particular interest are the Berger and JLK 180 grain bullets. If you look at these bullets side by side, it's hard to tell a difference between them. I believe the JLK bullet dies were made from the same set of prints as the Berger VLD,Design by Bill Davis of Tioga Engineering). So this begs the question, why would these bullets have different BC's? They're the same weight and the same shape. This is just the kind of smoke and mirrors that makes shooters think there is something mysterious about BC's and exterior ballistics that's beyond the realm of human understanding. I was pleased with the results of my testing of these two bullets: the BC is the same, as expected. All is right with the world.
Part of the reason there is so much 'slop' in advertised BC's is because they're referenced to the G1 standard which is very speed sensitive. The G7 standard is more appropriate for long range bullets. Here are the results of my testing for these two bullets:
G1 BC's, averaged between 1500 fps and 3000 fps:
Berger 180 VLD: 0.659 lb/in^2
JLK 180: 0.645 lb/in^2
The reason the BC for the JLK is less is mostly because the meplat was significantly larger on the particular lot that I tested,0.075" vs 0.059"; see attached drawing).
For bullets like these, it's much better to use the G7 standard. The following BC's are referenced to the G7 standard, and are constant for all speeds.
G7 BC's:
Berger 180 VLD: 0.337 lb/in^2
JLK 180: 0.330 lb/in^2
Many modern ballistics programs, including the free online JBM ballistics programs are able to use BC's referenced to G7 standards. When available, these BC's are more appropriate for long range bullets.
Take care,
-Bryan
Attachments
Brian:
Thanks for all your hard work and the education -- and your www.
I agree that the 7mm 180 Berger VLD and the 180 JLK VLD look to be about the same shape. But I have found a huge difference in the seating depth,into the lands). I find that the 180 JLK and the 175 SMK seat to about the same depth. With the same die setting, the 180 Berger and the 176 GTB seat MUCH deeper into the case. With all that said, the Bergers shot knots for me with ever load I tried.
Congrats on your article!
Keep up the good work,
Jim
Thanks for all your hard work and the education -- and your www.
I agree that the 7mm 180 Berger VLD and the 180 JLK VLD look to be about the same shape. But I have found a huge difference in the seating depth,into the lands). I find that the 180 JLK and the 175 SMK seat to about the same depth. With the same die setting, the 180 Berger and the 176 GTB seat MUCH deeper into the case. With all that said, the Bergers shot knots for me with ever load I tried.
Congrats on your article!
Keep up the good work,
Jim
Hi Bryan,
I read with interest your articale in PS for March,just got it delivered in the UK!) and was going to contact you regarding this.
Whilst my technical knowledge is somewhat limited I am very interested in actual B.C and ballistics, I shoot the 7mm Berger in UK National F class and find it an excellent bullet, I have found that Exbal will calculate the correct path and impact within 1/2 MOA at 1000yrds with the published B.C however I have not until now input the correct altitude, humidity and temperature, I have some new Ballistics software,Patagonia) which is very comprehensive and somehow uses the G1 and G7reference together, I have not had the opportunity to play with it in detail as yet.
My real question is: if the manufacturers B.C is incorrect how come I can get my software to predict accurately the impact when I input actual velocity etc, I am no way doubting your calculations, just wondered how to calculate bullet impact and path correctly from now on.
Finally the article was excellent and look forward to some more!
with regards
Gary
As a sidebar I have been experimenting with pointed bullets and found them to improve consistency but have had no real world improvement in lower elevation at long range, have your calculated the improvement in B.C with the 7mm 180 Berger at all?
I read with interest your articale in PS for March,just got it delivered in the UK!) and was going to contact you regarding this.
Whilst my technical knowledge is somewhat limited I am very interested in actual B.C and ballistics, I shoot the 7mm Berger in UK National F class and find it an excellent bullet, I have found that Exbal will calculate the correct path and impact within 1/2 MOA at 1000yrds with the published B.C however I have not until now input the correct altitude, humidity and temperature, I have some new Ballistics software,Patagonia) which is very comprehensive and somehow uses the G1 and G7reference together, I have not had the opportunity to play with it in detail as yet.
My real question is: if the manufacturers B.C is incorrect how come I can get my software to predict accurately the impact when I input actual velocity etc, I am no way doubting your calculations, just wondered how to calculate bullet impact and path correctly from now on.
Finally the article was excellent and look forward to some more!
with regards
Gary
As a sidebar I have been experimenting with pointed bullets and found them to improve consistency but have had no real world improvement in lower elevation at long range, have your calculated the improvement in B.C with the 7mm 180 Berger at all?
Bryan Litz Ballistics
Site $$ Sponsor
Gary,
Thanks for the feedback on the article.
I've got a likely explanation for your observations with the 7mm Berger 180 VLD. This is also the bullet I shoot in long range prone competition.
You say you haven't taken into account the actual atmospheric conditions when running ballistics programs. I suspect that your shooting is done in 'summer' like conditions, ie, warmer than 59 degrees F, above sea level, etc. If you used the advertised BC of .682,which is a little too high) and shot in conditions that were favorable,meaning lower air density) the combination of the two 'errors' would partially cancel each other out.
Here's an example:
Let's say you use a BC of .682,advertised value) and standard sea level conditions to calculate the trajectory, and it predicts 300" of drop at 1000 yards. The two errors are: inaccurate BC, and inaccurate atmospheric conditions. The two errors can be of very similar magnitude, and if they're opposite direction, will cancel each other out. This is not the recommended approach. Much better is to use a more accurate BC, and input the actual atmospheric conditions. This approach will be more reliable. Also, make sure you know the actual range to the target. Some ranges are supposed to be 1000 yards, but may actually be +/- 10 or 20 yards. This can have a noticeable affect on drop for someone who's paying attention.
All of this discussion is less relevant for F-class and prone shooting because we have sighters allowed. +/- 5" of drop isn't very important, just so we get on paper it's good. The error could have more of an impact for other types of shooting though.
Here's another thing to put it in perspective...
The 4% error,.659 vs .684) in BC for the B180VLD is not very consequential to drop, even at 1000 yards. The error causes a difference of 7" of drop at 1000 yards for 2800 fps muzzle velocity. This is a small amount when you consider everything else at play including vertical wind currents, etc. By comparison, it takes about a 20 degree F difference to cause the same vertical shift.
In regards to your ballistics program questions...
I think Exbal uses the traditional Siacci method as it's ballistics engine, just like Sierra Infinity, JBM ballistics, and most others. Patagonia uses a very different engine developed by Arthur Pejsa,who has an article on exterior ballistics coming out in the April issue of PS).
The traditional approach,Siacci method) uses the ballistic coefficient directly,whether it's G1, G7, etc) for ballistic calculations. The Patagonia solution has to convert the BC into a quantity that can be used by it's solver. If the time is taken to describe the BC's velocity variation, the Patagonia software can be just as accurate as the Siacci method, but it can be subtly complicated because the nature of the solution is different.
Speaking just in terms of accuracy, ballistics programs don't have to be complicated. The free online JBM program is as accurate as they get. I've verified the predictions of this code with my own 'Siacci' based solver, as well as an independent 'point mass' program, which uses numerical integration to solve the equations of motion. The accuracy of the solver is usually not what limits the accuracy of ballistic predictions, it's the accuracy of the inputs. For long range bullets, if you enter an accurate G7 BC, actual atmospheric conditions, actual range to the target, good zero range, etc, the results will be more accurate than most rifles. In other words, uncertainty in the results is directly related to the uncertainty of the inputs.
In response to your aside...
I have measured the B180VLD in both nominal, and pointed meplat configurations. Pointing the meplat from 0.059" to 0.039" increases the G7 BC from 0.337 lb/in^2 to 0.344 lb/in^2. This results in less than 2" difference in wind drift,10mph@1k yards). The improvement is small, perhaps negligible for standard decimal prone targets with large scoring rings. The improvement is more significant for the F-class targets with smaller scoring rings. That being said, I do point my B180VLD's that I shoot in prone competition. It's fast, easy, doesn't hurt anything, and every little bit helps.
Take care Gary,
-Bryan
Thanks for the feedback on the article.
I've got a likely explanation for your observations with the 7mm Berger 180 VLD. This is also the bullet I shoot in long range prone competition.
You say you haven't taken into account the actual atmospheric conditions when running ballistics programs. I suspect that your shooting is done in 'summer' like conditions, ie, warmer than 59 degrees F, above sea level, etc. If you used the advertised BC of .682,which is a little too high) and shot in conditions that were favorable,meaning lower air density) the combination of the two 'errors' would partially cancel each other out.
Here's an example:
Let's say you use a BC of .682,advertised value) and standard sea level conditions to calculate the trajectory, and it predicts 300" of drop at 1000 yards. The two errors are: inaccurate BC, and inaccurate atmospheric conditions. The two errors can be of very similar magnitude, and if they're opposite direction, will cancel each other out. This is not the recommended approach. Much better is to use a more accurate BC, and input the actual atmospheric conditions. This approach will be more reliable. Also, make sure you know the actual range to the target. Some ranges are supposed to be 1000 yards, but may actually be +/- 10 or 20 yards. This can have a noticeable affect on drop for someone who's paying attention.
All of this discussion is less relevant for F-class and prone shooting because we have sighters allowed. +/- 5" of drop isn't very important, just so we get on paper it's good. The error could have more of an impact for other types of shooting though.
Here's another thing to put it in perspective...
The 4% error,.659 vs .684) in BC for the B180VLD is not very consequential to drop, even at 1000 yards. The error causes a difference of 7" of drop at 1000 yards for 2800 fps muzzle velocity. This is a small amount when you consider everything else at play including vertical wind currents, etc. By comparison, it takes about a 20 degree F difference to cause the same vertical shift.
In regards to your ballistics program questions...
I think Exbal uses the traditional Siacci method as it's ballistics engine, just like Sierra Infinity, JBM ballistics, and most others. Patagonia uses a very different engine developed by Arthur Pejsa,who has an article on exterior ballistics coming out in the April issue of PS).
The traditional approach,Siacci method) uses the ballistic coefficient directly,whether it's G1, G7, etc) for ballistic calculations. The Patagonia solution has to convert the BC into a quantity that can be used by it's solver. If the time is taken to describe the BC's velocity variation, the Patagonia software can be just as accurate as the Siacci method, but it can be subtly complicated because the nature of the solution is different.
Speaking just in terms of accuracy, ballistics programs don't have to be complicated. The free online JBM program is as accurate as they get. I've verified the predictions of this code with my own 'Siacci' based solver, as well as an independent 'point mass' program, which uses numerical integration to solve the equations of motion. The accuracy of the solver is usually not what limits the accuracy of ballistic predictions, it's the accuracy of the inputs. For long range bullets, if you enter an accurate G7 BC, actual atmospheric conditions, actual range to the target, good zero range, etc, the results will be more accurate than most rifles. In other words, uncertainty in the results is directly related to the uncertainty of the inputs.
In response to your aside...
I have measured the B180VLD in both nominal, and pointed meplat configurations. Pointing the meplat from 0.059" to 0.039" increases the G7 BC from 0.337 lb/in^2 to 0.344 lb/in^2. This results in less than 2" difference in wind drift,10mph@1k yards). The improvement is small, perhaps negligible for standard decimal prone targets with large scoring rings. The improvement is more significant for the F-class targets with smaller scoring rings. That being said, I do point my B180VLD's that I shoot in prone competition. It's fast, easy, doesn't hurt anything, and every little bit helps.
Take care Gary,
-Bryan
Hi Bryan,
What a great reply, I did realize that atmospheric conditions were required and important and have just purchased a Kestrel Anemometer, which I have even managed to calibrate using google earth!
You are correct in saying most shoots for long distance have been in warmer conditions, I will be shooting this weekend in a National so I will try the new BC with all three programs with correct atmospherics and see,, I will let you know the results) It actually snowed here over the weekend over 3" so the weather will be on the cool side.
With regard to the pointing, 2" is enough if your on the line! particularly with the newer tight targets could mean the difference between a 4 or a 5,or in the U.S a 10 or a 9!) as yourself I all ways point as it seems to help and will continue to do so.
I really appreciate your time and information,and without being nosey do you study ballistics out of interest or is it more of a profession.
Again thankyou and good shooting.
Gary
What a great reply, I did realize that atmospheric conditions were required and important and have just purchased a Kestrel Anemometer, which I have even managed to calibrate using google earth!
You are correct in saying most shoots for long distance have been in warmer conditions, I will be shooting this weekend in a National so I will try the new BC with all three programs with correct atmospherics and see,, I will let you know the results) It actually snowed here over the weekend over 3" so the weather will be on the cool side.
With regard to the pointing, 2" is enough if your on the line! particularly with the newer tight targets could mean the difference between a 4 or a 5,or in the U.S a 10 or a 9!) as yourself I all ways point as it seems to help and will continue to do so.
I really appreciate your time and information,and without being nosey do you study ballistics out of interest or is it more of a profession.
Again thankyou and good shooting.
Gary
Bryan Litz Ballistics
Site $$ Sponsor
Gary,
I'll be most interested in your results. It's important to have a good zero so you know how much the drop really is. Also, the accuracy of the scope,or iron sight) adjustment is important when doing these things.
To answer your question, ballistics is both a profession and a hobby for me. My full time job is air-to-air missile design engineer so I'm very familiar with supersonic aerodynamics. Aerodynamics is simpler for bullets than missiles, for the most part. An exception is the subtleties of 'spin' stability vs 'fin' stability.
I've also got a part time consulting business called 'Applied Ballistics, LLC'. I specialize in bullet design, ballistic program development, and external ballistic testing. I don't have a website for the business yet, I've been busy enough without advertising so far.
I'm also very active in NRA long range prone shooting.
Good luck at your F-class nationals, we await your results.
-Bryan
I'll be most interested in your results. It's important to have a good zero so you know how much the drop really is. Also, the accuracy of the scope,or iron sight) adjustment is important when doing these things.
To answer your question, ballistics is both a profession and a hobby for me. My full time job is air-to-air missile design engineer so I'm very familiar with supersonic aerodynamics. Aerodynamics is simpler for bullets than missiles, for the most part. An exception is the subtleties of 'spin' stability vs 'fin' stability.
I've also got a part time consulting business called 'Applied Ballistics, LLC'. I specialize in bullet design, ballistic program development, and external ballistic testing. I don't have a website for the business yet, I've been busy enough without advertising so far.
I'm also very active in NRA long range prone shooting.
Good luck at your F-class nationals, we await your results.
-Bryan
The Cauterucio's now weigh 189 grains, and are visibly longer then the 180 Bergers - I can't post a picture until I get back home from out of town on Friday night - and look somewhat similar. According to Bob, his stated BCs are the result of feedback from people shooting the bullets, not from a software prediction. When I shoot mine,sometime in the next few weeks), I'll post feedback on the elevation and windage results as compared with the Berger 180s in my 7WSM.
JeffVN
JeffVN
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