Comparing stability and ballistic coefficient
I was playing around with the Berger Twist Rate calculator, and came upon something interesting. Berger recommends using a bullet with an SG of 1.5 or greater for maximum stability. However, bullets between an SG of 1 and 1.5 are classified as “marginally stable.” Berger says you may get good groups, but you won’t be able to take full advantage of the bullet. Here’s where it gets interesting. Take this scenario for instance, using a 1 in 11 twist .30-06.
According to the Hornady reloading manual, a 168 grain ELD Match bullet has a G7 BC of 0.263. At a maximum velocity of 2800 fps using the max charge for H4350, it has an SG = 1.81.
That same manual states that a 200 grain ELD-X has a G7 BC of 0.301. At a maximum velocity of 2500 fps using the max charge for H4350, it has an SG = 1.22, and an adjusted G7 BC of 0.276.
Now, according to the calculator, the 168 grain bullet has greater stability, and the 200 grain bullet, while having lesser stability, is not classified as “unstable” (SG = 1 or less), and it has the greater G7 BC. I realize BC isn’t the end-all, be-all, but I’m using it as a reference point.
There’s many different combinations to compare. Is there a point where having less stability, but not being unstable, is outweighed by having a higher BC? Or is it always better to go with the higher SG, at the expense of BC and heavier weight bullets? Does it depend on the range and cartridge you want to shoot, and if it does, is there a cut-off point where you should choose one over the other?