The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

Hi all,

The F class rounds I'm loading are using 155 Gn Bergers, PN:30426.

On the box of bullets it quotes G7 BC=2.47 G1 BC=.483

I think the BC relates to ballistic coefficient buyt why the two different numbers on the same box?

Thanks,

Mick.

The BC figures are how the bullet compares to the reference projectile, G1 and G7 are two different reference projectiles so they give two references. Wikipedia has some info.

Basically if they publish G7 data,use it - much more accurate for bullets which are close to G7 reference shape. It is much closer to the BT VLD shape.

Additional to the above, ballistic calculations based on G7 BCs give better results over a larger range of velocities, so they are particularly better suited to long range shooting where much of the velocity is lost between muzzle and target. Given the choice, look for G7 data bade on third party measurements rather than the claims of the vendor.

..

Even better check the velocity both at the muzzle and the target and from this you can work out the BC of your bullet from your rifle at your local range, from this you can very accurately predict the drops required for different distances and in varying conditions. I point my own bullets and am constantly playing around with different tip tooling so knowing both MV up and down range is essential if I am to confirm the effectiveness of the tipping.

Of course, it is only useful info if it is right....2.47 for that G7 BC isn't right.

The #30426 declared G7 is .247, my view is it is closer to .241 un-pointed, maybe even a tad less.

How do you check the velocity at the target? A chronograph in front of the target or some kind of sensor built into it?

I use an acoustic chronograph at either end. I prefer them as they have a larger sensing range and a low profile so harder to shoot....

Davy how do you figure out the BC from that data?