Range Report BCs stated value

[dar1246]

How do the bullet manufactures derive the BCs. I read on Lapua's site and they use a Doppler Radar. Do all the manufactures use the same?

If this is the case. Why do the lapua 139s show less than A-Maxs. But yet on the stated BC the lapuas are higher.

 

[BryanLitz]

Re: BCs stated value

All manufacturers use different methods of determining BC.

Lapua's use of doppler radar is probably the best, but when they state a BC they only give a value that's valid for high speed. Since G1 BC decreases as the bullet slows down, the <span style="font-style: italic">average</span> BC of the bullet is much less than the single value Lapua states for high velocity.

Sierra gives G1 BC's in velocity bands to account for the decay effect.

Berger gives an average G1 value and a G7 BC. The G7 BC is a better fitting drag model for long range bullets and doesn't decay over distance like a G1.

You can read more about G1 and G7 BC's here:
http://02b0516.netsolhost.com/blog1/?p=62

In my book, I've measured and published G1 and G7 BC's for 175 long range bullets from all brands and common calibers. These were all measured the same way, by the same source and are very accurate.

Take care,
-Bryan

 

[dar1246]

Re: BCs stated value

That is what I read on Lapua's site also. That the BCs will vary at different speeds. It also can be used with Quick Target.
http://www.lapua.com/uploads/media/LapuaBulletsDragCoefficient.pdf

I do use the G7 in my programs and it works great. That makes more sense. Why not published both on the same box or web site like bergers bullets.

Thanks Bryan

 

[Rovieairto]

Re: BCs stated value

I've noticed that the A-max bullets often have a flatter trajectory than comparably driven HPBT's.

Whatever numbers that the MFG's use are of little importance as results are all that matter to me.

I think that the doppler method may be the best way to get accurate ballistic data but the number that Lapua uses to define their BC usually seems high.

Brian, your book looks fantastic!

 

[Rob01]

Re: BCs stated value

I would recommend Bryan's book for anyone shooting long range. Full of excellent info and true, tested BCs.

 

[Swan]

Re: BCs stated value

Just received my copy of the Litz book. I am very impressed with the data, and just started reading the first chapters. Highly recommend getting this book.