Just struggling to keep up with this stuff.
The Berger manual simply describes SD, FF, & BC. The other bullet manufacturers manuals seem to boost BC values to market bullets - customers scanning lists of bullets looking for those with highest BC values; not Berger.
Looking at the time of flight for a bullet to reach a target, (at least at the distances where most people shoot, 1000 & under, all super sonic bullets) the spin rate decay would be next to zippo and of no practical consequence. But then again some target might just be several miles away and the spin rate decay would be a factor - I have no plans to get into that stuff.
Should there be something to shoot at on the moon, with all those craters, I would go for a round ball to achieve the best practical cost effective uniform results - nice round holes in targets.
Looking at previous posts, I noted that, upon occasion, bullets having lower BC values, out performed bullets having higher BC values. In one comparison G1 BC values were used to describe both bullets, apparently some 6.5 and a 210 gr. Berger .308. The G1 BC's for the 210 Berger bullets are .626 & .631 (as per circa 2013). The highest G1 BC for any 6.5 target bullet that Berger makes is .618 (as per circa 2013). Was an assigned, apparent G1 BC value of .670, correct for the 6.5 bullet, if it was a Berger bullet? If the G1 BC was .670, might the bullet be some real long heavy 6.5 having a slower MV than the .308 210?
Am I right with this?
The SD or sectional density, SD = (bullet weight in grains/7000) / (caliber ^2)
; G7 BC = SD / FF
; G7 FF = SD / G7 BC
The form factor being a measurement of drag as compared to a standard G7 value of 1
Plugging in some numbers of various calculations, using one of my favorite bullets, 95 6mm Berger VLD, as a standard :
G7 BC = SD/FF = ((95/7000)/.243**2) / .923 = (.0136/.0590) / .923 =
.248, this agrees with table page 169, Berger manual
Another BC calculation in this thread:
While you guys ponder on this, remember a couple of things.
1) BC in and of itself is calculated in part using weight. BC = (weight in grains / 7000) / ( caliber ^2 * form factor).
2) Lag Time is important.
3) Since lag time is important, Muzzle velocity is also very important. Bullet weights have an impact on our ability to obtain the same muzzle velocity depending on your cartridge selection. Also remember a BC is true at a given velocity.
4) Bullets are not "pushed" by the wind, they are actually pulled by drag. Wind changes the orientation of the gyroscopically stabilized projectile, and a small amount of drag is shifted pulling the bullet off course.
This matches
What's "lag time"?