Just to be clear, when using the drag program to calculate a ballistics table, it it NOT using the G7 ballistic coefficient. This program does not use ballistic coefficients from drag curve data from a standard projectile, G1, G7 or otherwise to calculate the ballistics table. Instead, it calculates the drag curve directly using Bob McCoy's formulae. (Bob McCoy worked at the Aberdeen Proving Ground in the USA and was a very highly regarded ballistician, who wrote what is widely regarded as the standard text on external ballistics.)
Why Use Multi BC's when modelling trajectories of highly efficient Lead Free Bullets
- Thread starter Yew Tree Fieldsports
- Start date
Robert McCoy was THE ballistician pretty much, I have his book sat on my bookshelf and refer to it often.
At the end of the day the program has calculated the drag curve from bullet dimensions. In terms of drag curve data or either G1 or G7 BC the results indicate to me that at higher velocities (mach 2.5 + ‘ish’) the formulae/algorithm used underestimate the efficiency of the bullet.
Utectok
Well-Known Member
I think this theoretical discussion is really interesting although the data @Yew Tree Fieldsports provides is more than adequate for stalking and for the longer range gong bashing as a start however local conditions often dictate a couple of clicks more or less is required? This can only be established on the range? theoretical bullets only get you so far… anyway that’s been my limited experience.
This seems likely to me. I do suggest that you at least skim the Hornady 4DOF paper I previously referenced. It is a good read. https://press.hornady.com/assets/site/hornady/files/ballistic/hornady-4dof-technical-paper-v2.pdf
E.g. on page 3 they show dramatic differences between a variety of their bullets, and the standard G7 curve. Drag measured with doppler radar.
Their 6mm BTHP seems to go much better than a G7 BC would suggest. The 338 ELD-M is an almost perfect fit. And so on.
I think that to model drag more for the precise details of a specific bullet (or other projectile) shape and features would require sophisticated computational fluid dynamics. Which I suspect nowadays is quite possible. But not necessary for this sort of application.
It does seem that @borbal 's modelling gets more than close enough to be helpful, particularly for a bullet manufacturer wanting to experiment with ideas before cutting metal and testing at a range.
On page 11 it does become quite esoteric, showing how the same bullet shot from different barrels can behave differently. No substitute for testing in your own rifle to find out how things deviate from theory or somebody else's testing.
Alan_Hayes
Well-Known Member
Well and truely lost proper geeky stuff, but I do know the bullets work well. So that’s enough me. Cheers Rich.
Just to let those that are interested know that the TLR bullets are now available in the Strelok database.
No because I haven’t done detailed work Bc wise on any of the hollow points and don’t intend to. The ballistic solutions are for the TLR’sHi just had a look on the Strelok Pro but the 6.5 in 112g G1 is not there as yet , has this been sent over to him mty
Thanks
Cheers
Rich
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