BC Variation bullet to bullet is real, and its a problem.

[graywolf]

How is the 156 EOL shaping up (pardon the pun)?

 

[DocUSMCRetired]

How is the 156 EOL shaping up (pardon the pun)?

0.5%. Well below the 1% mark at a BC SD of 0.002.

 

[graywolf]

Thanks- I also saw some anecdotal field reports that the 156 EOL G7 was actually higher than the value Berger is listing. Anything to that? I have only shot these out to 300 so far but they are exceptionally accurate.

 

[DocUSMCRetired]

Thanks- I also saw some anecdotal field reports that the 156 EOL G7 was actually higher than the value Berger is listing. Anything to that? I have only shot these out to 300 so far but they are exceptionally accurate.

They just used a conservative average estimate. In our lab testing we got a G7 Average BC of 0.355. It isn't technically a wrong number that is printed on the box, but we have an article coming out that will show why pretty soon.

 

[DocUSMCRetired]

Touching up some more on this thread, here is our latest article which does cover this subject in part. http://appliedballisticsllc.com/Art...rms – Improving on Ballistic Coefficients.pdf

 

[graywolf]

That is a great analysis, it makes sense to use of all of the RADAR data obtained to get the CDM and also track the G7 variance. It gets even more complicated when you consider the variance is affected by velocity. But in general how does the effect of G7 variance on vertical dispersion compare to the effect of muzzle velocity variance? Certainly it depends on the specific case but for typical bullets you've looked at, say 1% variance in G7 and 1% muzzle velocity variation, is the effect of the BC variance on target dispersion significant?

 

[PApa Black]

BC Variation from bullet to bullet in the same box is something that is hard to detect with short range work but the further you try to shoot the more that problem compounds. We have been providing shooters who get PDMs a print out which shows this variation. We will have more on this topic in the future but picking a high quality and consistent bullet will help minimize this problem.

Great post Doc! Thanks!

 

[DocUSMCRetired]

That is a great analysis, it makes sense to use of all of the RADAR data obtained to get the CDM and also track the G7 variance. It gets even more complicated when you consider the variance is affected by velocity. But in general how does the effect of G7 variance on vertical dispersion compare to the effect of muzzle velocity variance? Certainly it depends on the specific case but for typical bullets you've looked at, say 1% variance in G7 and 1% muzzle velocity variation, is the effect of the BC variance on target dispersion significant?

You could actually run the numbers fairly easily at a specific target distance. Simply adjust the BC +/- by that percentage and run it as a calculation. That will give you the high and low dispersion.

In fact I did it with the bullets in this article. One of the tested bullets has an ES of 0.011 or 3.6%. SD of 0.008 or 2.5%. So what I can do is take the low and highs of the ES and just run the calculation at 1000 yards. This gives me 24.64MOA and 25.75MOA. 1.11MOA of spread. Now if I take the other bullet and run its highest and lowest data points using the EXACT same target data you get. 26.52MOA and 26.35MOA. This gives you a spread of about 1/4 MOA. This is how the data was actually derived for the article. I simply ran the firing solution at 1000 yards given the exact same target data and inputting the high and low measured BC.

If you do it with the SD then you can see where 90% of your shots should be. If you do with the ES then you see the actual spread of that particular volley. Relatively speaking that is, because if you look in the article you can see at least 4 outliers in one of the test volleys, and looking at another set of data on that bullet but in a different caliber it showed the same results. So it is also bullet dependent, and not as simple as it looks on paper.