I thought a BC was the same as any other BC.
But from reading some documents I've found there's different ways to measure BC that result in very different numbers.

This is the document I was reading: www.appliedballisticsl...Update.pdf

The round I'm looking at using has a G7 BC of 0.236 or a G1 BC of 0.462.
But which one should I use in Point Blank?



Grrr, just when I was thinking I was starting to understand the basics.......

The G7 and G1 refer to bullet shapes; boat tail vs. flat base. That should help you decide which to use. I just use the BC the bullet manufacturer gives. A BC changes a bit when the velocity velocity gets around the speed sound but for most of us that isn't an issue (except with .22 rimfires).

I thought that a boat tail has less drag and a better BC then a flat base.
If so, then why is the BC for G7 less then for G1?

How how will Point Blank know which one is which?

The manufacturer of this bullet doesn't give a BC. So short of using a chrony at the muzzle and at 100yd and inputting that into Point Blank (assuming I don't destroy the chrony!) I have these two measurements that the guy took off the shape of the bullet itself.

I shouldn't hit the transition of the sound barrier. This rifle will be shooting out to 1000yd with .308win with a 26inch barrel.

What bullet are you using?

Thinking of trying the Dyer HBC. An Aussie made product. 1000 for $360 from the Victorian Rifle Association.

It's one of the approved pills for F Class standard.

From what I gather it's just a bit more then a backyard factory setup, but the bullet is very favoured for it's excellent BC.

Pumpkinslinger,
The formulas for calculating the various B.C.'s are different. If you plug a G7 B.C. into a program that's expecting a G1, it will not give you accurate results.

Unless otherwise stated, most programs use the G1 B.C. Not an authoritative answer, but I believe PB uses the G1 model.

PointBlank does use the G1 drag functions.

The only true way to know the BC of your bullet is to fire it out of your rifle and compute it. PointBlank actually does have the functionality to calculate your BC based on muzzle and 100 yard velocities. It will compute the proper value based on velocity fall off over that distance.


-DallanC