Re: G1 vs G5 calculating BC?
The purpose of a ballistic calculator is to help you get on or near paper at long range and once you find your real world data such as drag model and BC this allows you to accurately and reliably predict where your bullets will impact in different atmospheric conditions. Real world testing is needed to get the best drag model and BC.
In my experiance, it depends on the bullet AND the rifle it was fired from. For example, the 155 SCENAR in theory should be a G5 or even G7. In my "real world" tests with one rifle in particular, a G1 model of .499 matched the RSI program and TRA near perfect. The 178 AMAX in the same rifle was best used with G5 and .318. These numbers were not figured by programs or guesses but actual tests.
With the differing velocities we shoot bullets, barrel quality and twist rates it can be near impossible to predict an accurate drag model and BC and IS impossible to accurately predict one number for everybody to use with any reliablity.
My advice is start with G1 and the factory number and go out in the field and start there. You may be right on or not. You in MOST cases will get on the target somewhere. Once there, you can work into the bull's eye and document the difference. Then go home and work the numbers on your program. You will find a "G" function and decimal number to coincide with your tests. This is what you will use for future ballistic calculations.
Also get used to the fact that higher G numbers ussually have lower BC numbers. This doesnt meen the bullets will fall off the table. In my previous example between the 178 and the 155 you will notice the HUGE difference in the decimal number yet when I used the G1 model with the 178 the number was somewhere around .5 (I dont remember exactly) and that got me from my 300 yard zero to 1000 yards. The problem was the ranges in between my zero and 1K and the impacts did not match the calculated drops. When changed to G5 and .318 everything matched with near perfection. I think the worst number on the calculated drop chart was less than 2" off the mark from the real world drops at 700 yards.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
Last edited by Michael Eichele; 12-14-2008 at 10:27 PM.