I am changing. Specifically, for LRH I'm shooting VLDs and changing to software using G7 BCs for ranges where the retained velocity is less than 2,000 fps. AND this second edition contains 225 independently measured BCs (hint not company advertised). That's what I think I know, anyone out there know something better ? What is LAG TIME, DANGER SPACE and who is John Galt ?
Somewhere Between Ignorance & Arrogance,
CRaTXn
All G() funtions are bullet models. The G1 model is for a not very aerodynamic flat base projectile with a short spitzer ogive. It works fairly well for short range benchrest and varmint bullets.
The G7 model is is for boattail bullets with long radius ogives. It works well for most VLD bullets. If measured values are available for both models it makes sense to use the one which is closest to the bullet you're using. It's not always obvious just from looking a a bullet which will be the better match. Bryans book is useful in that it gives values in both systems for many popular long range target and hunting bullets. For those you have a choice of using G1 or G7 tables, and you can tell which is the better match from the data he gives for those bullets.
I don't understand though why the talk of "changing". If a bullet hasn't been measured for it's fit to the G7 system theer is no simple formula that you can apply to a G1 BC to convert it to a G7 BC so that it will be a better fit.
What is a better method? A better method would be for each bullet manufacturer to measure (or calculate) and publish drag vs velocity tables for each of their bullet models. If it was handled all in software it would be as easy as using BC's and more accurate. Will it happen? Not likley. Bullit manufactures like G1 BCs because the masses will buy a bullet with .636 BC sooner than one which has a .455 BC or one which just has has a downloadable drag table called 308-190-SMK.dat. Many shooters don't worry about it.
The BC assigend to a bullet makes no differece in how it flies, only how the ballistic program's simplified equations say it should fly. They will alwasy have built in errors. Using drag tables won't fix the errors which the computer models don't address at all. Reality is that G1 BC's are "good enough" for most practical shooting since for most shooters wind estimation limits accuracy more than anything else.
What is LAG TIME. It's the difference in seconds that a bullet actually takes to reach the target minus the time it would have taken if the same shot was fired at the same muzzle velociy without atmospheric drag. Lag time multiplied by crosswind velocity is equal to bullet deflection at the target if consistant units are used. That is callled Didion's equation. You'll find that equation imbedded in all of the ballistics programs in common use today. Usually just one line of code. BCs only play a part in that equation if you use them to calculate the actual time of flight to the target. BC's are not needed to calculate wind deflection if you simply measure the time of flight rather than calculate it.
What is Danger Space - I don't have a clue.
Who is John Galt - A fictional charater in Ayn Rand's novel Atlas Shrugged As a young electrical engineer he invented a fictional electric motor with a fictional power source. (Ayn was not an engineer). In the book he also started a labor strike among engineers, inventors, and corpoaration builders to fight a corrupt government. It's surprising applicable to todays situation though it was set in the 1950's,