Good luck!
*******************************Tech Corner
If you want to figure out the G7 or any other number for a bullet like the Sierra bullet in the table above, you can get pretty close using the free JBM online calculators. Look at the middle two BC numbers in the table. They have both upper and lower velocity limits. Pick one of those two ranges. Use its limits with JBM's trajectory calculator for the G1 BC. Note the distance traveled starting at the first velocity and ending at the next. Now plug those same two velocity limit numbers and the distance you noted into JBM's BC calculator and pick the standard you want the new BC for (G5. G7, etc)? The returned number should be close and in trajectory programs that have the other BC types available to use, should give you better trajectory predictions outside that velocity range than the G1 BC does.
For example: Using the first BC limits of 2600 fps and 2100 fps and the G1 BC given as .447, I run the JBM trajectory table for G1 in one yard increments to 300 yards (enough to drop to 2100 fps). I start with a muzzle velocity of 2600 fps, setting the chronograph distance to zero. The resulting table starts at 2600 fps and scrolling down I find 2101 fps at 262 yards, and 2099.2 fps at 263 yards. I extrapolate to get 262.6 yards as the point at which velocity was 2100 fps.
Next I go to the velocity-based ballistic coefficient calculator. I plug in a start velocity of 2600 fps and an end velocity of 2100 fps. I put 262.6 yards (don't forget to select yards; default is inches) into the distance. I run it once with the G1 number selected to be sure it returns the same 0.447 BC I started with. If not, I've entered something wrong somewhere. But in this case it does return 0.447. Next I select the form I want. In this case G5 looks closest. G7 is for VLD shapes. I get back 0.228. So the G5 BC for this bullet is 0.228. Now I can go back to the first trajectory calculator and set it to work with G5 BC's and enter .228 and get a more accurate trajectory table than I would with .447 and the G1 BC.
