G7 bullet BC's source?

[Travelor]

It appears that the G7 tables/programs are proving to be more accurate with the bullets we are shooting these days. Thanks to Brian Litz.

I am at a loss to find the G7 BC's for the bullets I am using using. Does anyone have a source for BC's for Sierra and Berger bullets with the G7 value?

Also, which program/programs are you using to compute your ballistics using the G7 models? I have the Sierra and QuickLoad/Target programs and they seem to ONLY use the G1 computations. I do see that the JBM program will use G7 BC's

Merry Christmas,

George Toney

 

[Laurie]

George,

you can ask around for G7 BCs for any bullet you are interested in from other forum members.

If you're using Bergers, the company lists the G7 value for its models (plus the G1).

If you're using .308" 155s, there is a full Bryan Litz analysis on a free online shooting magazine - www.targetshooter.co.uk. I can't remember the issues they're (it's a 2-parter) are in. I think some of his other articles can be downloaded too from various sources. Look on his website - see below.

Finally, you can buy Bryan's book which comes with a simple G7 ballistics program on a CD. The book is well worth having in itself as it is mine of valuable information for any long-range shooter, and has the i7 and G7 values of 175 or so long-range bullets listed from .224" TO .338" calibres from all major makers, both match and hunting varieties. Moreover, these are not computer generated, but based on his own long-range tests measuring intermediate bullet travel times at a number of evenly spaced points.

Information and online ordering here

http://www.appliedballisticsllc.com/index_files/Book.htm

$39.95 + Shipping.

I keep my copy close at hand - I seem to have a need to refer to something or other every few days.

However ....... you don't say what range(s) you're shooting over. The better G1 programs are fine for up to 500/600yd IMHO.

For instance:

0.308" 155gn Lapua at 3,000 fps under standard environmental conditions:

600yd
Sierra Infinity VI: 1,981 fps; -72" drop over 100 zero; 24.5" deflection in 10 mph X-wind
Litz: 1,894 fps; -75.5" drop; 27.4" deflection

1,000yd
Sierra Infinity VI: 1,445 fps; -288" drop; 79.3" deflection
Litz: 1,299 fps; -311" drop; 91.7" deflection

On wind which is the most important thing for target shooters, the 600yd defelection difference is just under a half-MOA, but it would be a rarity for wind gusts to be varying by a full 10mph and running at exactly 90-degrees to the bullet path.

The 1,000yd deflection difference between the two is greater running at running at 1.2-MOA. One's predicted come-up from a 100yd zero now varies by 2-MOA which can start to lead to problems given typical errors in scope sight click-values.

Laurie,
York, England

PS Have a good Christmas yourself

 

[Steve Blair]

G7 BCs are usually computed from empirically derived data. It could be a series of chronographs or, if you have the money, a continuously tracking, doppler RADAR system.

QuickLOAD does not show ballistic data in its interface, but the data is contained in QL files. If the G7 is available, like for most Berger bullets, that data will be loaded into QuickTarget. The attached screen shot shows the "Drag Model" drop-down list box where you can select it. (upper right corner of the active window)

You can also approximate the G7 for a bullet where only G1 is supplied. Print the table for a G1 projectile to 1000 yards or meters in 100 yard or meter increments. Enter a G7 value for the same projectile and click "calculate". Keep iterating until the trajectories closely coincide. That will give you an approximate G7 value. Bryan Litz would probably have me hanged for that statement.