Ballistic calculator

[ctrout]

I am using the ballistic calculator at Ammoguide.com and have a question. There is a variable in the ballistic coefficient window that has several choices such as G1, G2, G5, G6, G7, G8, GI, and GL. I am usually doing calculations for centerfire rifle cartridges at velocities from 2500-3500fps. How do I know which variable to use?

 

[222Rem]

From:Sierra Ballistics


The G1 drag function is the best standard drag model to use. We have tested several drag functions,G1 for sporting bullets; GL for lead bullets; G5 for boat tail bullets; and G6 for flat base, sharp pointed, fully jacketed bullets). For each drag function we have measured BC values referenced to that function and observed how those BC values change with bullet velocity. We have chosen G1 because the changes in BC values with bullet velocity are least, and because there is a vast database in the literature on BC values referenced to the G1 standard. Also, to our knowledge all projectile manufacturers refer their published BC values to the G1 drag function, which facilitates comparisons among bullets of different calibers, weights, shapes and manufacturers.

To find more on ballistics use Google

 

[glo]

I just ran some numbers on www.eskimo.com/~jbm/calculations/traj/traj.html. The permeters: Berger 6mm 95gr. VLD; BC.514; muzzel velocity 3000fps. The ballistic read-out is as follows: G1-.524; G2-.266; G5-.340; G6-.293; G7-.309; G8-.256; GI.527 and GL-.641.

I'd do as Sierra does and stick with G1.

 

[ctrout]

Thanks. That's what I've been doing but the other inputs were so amazingly optimistic that I was hoping they were the more accurate options.

 

[js223]

You might want to read the articles on BC in Precision Shooting magazine by Bryan Litz. He makes a case for G7 being the best match for boat-tailed match bullets. Finding the G7 BC takes more work though, since you can't just use the advertised BC like with G1. However, if you are using a bullet tested by Mr Litz, his articles provide the G7 BC as well as G1.
The site mentioned by glo is a good one for calculations.