Good one, thanks. Use a specific gravity of 8.93 for copper monometal bullets.

One should keep in mind that twist calculators present the minimum twist rate for a given bullet. Shooting within 500 yards one can use any twist faster than the minimum without a problem. (unless you are pushing the bullets close to their structural limits)

Paul, this is where the McCoy calculator, given here, differs from the Miller and Greenhill systems. One can vary the twist rate with this system and there are graphs that give the stability factor and so on. This is a more accurate and very flexible system.

Paul
It helps if you know the stability factor that typically works in the application you are exploring.
Perfect bullets (swaged or machined) are much more tolerant of twist variations. Cast BPCR bullets are not perfect. They typically have internal defects that affect dispersion due to excessive RPMs. The BPCR guys often use bullets with minimal stabilization to 1000 yards. A slower twist will yaw and give oblong holes at those ranges. A faster twist gives excessive yaw when the bullet exits due to its internal imbalance.

You might check out that calculator and besure to specify a rifling twist. Look at both non-linear graphs. They are different than other calculators.

quote:

Originally posted by PaulS:
One should keep in mind that twist calculators present the minimum twist rate for a given bullet. Shooting within 500 yards one can use any twist faster than the minimum without a problem. (unless you are pushing the bullets close to their structural limits)