G1 and G7 on nikon BDC calculator site

[leo158]

What are the G1 and G7 used for? I noticed it changes yardage distance by a considerate amount. Any info will be appreciated. Thanks , Dan

[BoilerUP]

G1 and G7 are ballistic coefficient numbers, and are available from bullet manufacturers for a given caliber/weight/design buet.

[darkker]

What are the G1 and G7 used for? I noticed it changes yardage distance by a considerate amount. Any info will be appreciated. Thanks , Dan

To Expand on Boiler's exp a bit:
G1 is the standard expression for drag, or "how well" the bullet cuts through the air. It is based off of the "old standard" for measuring drag. The "Standard" projectile doesn't resemble many bullets used today however.

Not sure who officially gets credited with G7, but certainly popularized by Brian Litz.
There is NO ONE standard that fits all bullets. Match bullets, for the most part, are better represented by the G7. There are something like 8 different drag measurements, depending upon projectile.

I'm sure this is not 100% accurate, but it will give you an idea:
G7 is an ACTUAL measurement of drag, whereas G1 is a function of drag. For many bullet companies, they "calculate" what the drag is. However bullets don't have one figure, it is dependant upon speed(many other factors as well). This is why Sierra lists several G1 coefficients, based upon velocity. If you only see one G1#, it is an average calculation, meaning for any 1 velocity window; the number CAN be off quite badly.

[jpdown]

Berger is the only bullet manufacture I've seen who list the G1 and G7 ballistic coefficent for their bullets. They claim the G7 gives a more accurate flight path when using a ballistic calculator program that accepts the G7. As stated by darkker, the G1 can be misleading when used in a ballistic calculator and impact points at longer distances should be confirmed in the field. The G1 BC is usually a larger number and so most bullet manufactures list it in order to sell more bullets.

[BoilerUP]

Bryan Litz says G7 is more appropriate for modern boat-tail bullets.

[leo158]

So the ballistics should be close to what is said in the G7? Thank you all for replies, Dan

[darkker]

G7 will be a closer representation with current match bullets, Yes.

There is an exception however, that Litz has acknowledged. That is when you cross into Trans-sonic range, at that point the G1 becomes a better description.

I use Sean Kennedy's "Shooter". G7 works much better for 1,000 yard shooting for me, untill I go for 1200 yards. Then things get wacky, due to dropping out of super-sonic around 1150 yards.
I'm sure that alot of that has to do with the bullets stability, and boat-tail when crossing the trans-sonic range.
The old time POS tail angle of the 168 Sierra bullet didn't allow that bullet to survive the crossing. I'm pretty sure that it has been changed, but ask Sierra to be sure.
MOST match bullets use a 7-9 degree tail in order to survive that range.