Berger 215 twist rate??

SnowbirdUT

Well-Known Member
Joined
Jan 30, 2015
Messages
56
Location
Salt Lake City
I am not saying I disagree with you, I have read much about this topic from Brain Litz's articles and books. Just wondering why Hornady would post this on their website "
30 Cal 225 gr. ELD Match
1 in 10" Twist

0.777 G1
0.391 G7

0.752 G1
0.378 G7

0.719 G1
0.362 G7

30 Cal 225 gr. ELD Match
1 in 7" Twist

0.798 G1
0.402 G7

0.782 G1
0.393 G7

0.749 G1
0.377 G7
The 3 different groups of BC's for each twist rate is based on 3 different avg Mach speeds (Mach 2.25, 2.0, 1.75)
I will try to answer your question:

“ Just wondering why Hornady would post this on their website“

Drag on a bullet (aka Wind Resistance) is nonlinear. A Ballistic Coefficient is a measure of a bullets ability to overcome wind resistance or drag. The higher the number, the more aerodynamic the bullet and the better it will fly.

A quick aside, the difference between a G1 and G7 BC is that a G1 better approximates the drag of older flat based bullets. I use G1’s for my muzzleloader bullets. G7 better approximates the drag of newer boat tail bullets. Most of the bullets used by the people on this website in center fire applications are more modern boat tail designs that are better approximated with G7 drag models.

The wind resistance on any bullet decreases as the velocity increases. Most G7 BC’s quoted are an average drag over a range of velocities say from 3500 fps to 1200 fps. The Applied Ballistics calculator offers “custom BCs” that approximate the BC over infinitely small changes in velocity through transonic velocities.

It appears that Hornady is offering a range of BCs based upon velocities or Mach numbers. Some shooters may have much higher MVs at higher altitudes than other shooters with lower MVs at lower altitudes. This is useful information for some shooters but it is more of a marketing gimmick (my opinion only). A more useful measure of BC is one that is done the same way for all bullets in the survey population. Litz publishes a list of BC’s for 600 or 700 bullets. All the BC’s are measured the same way so it is useful for comparing bullets by the same manufacturer or between manufacturers.
 

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