spitballer
Member
The more over bore a cartridge is the slower a powder it will like...
I would agree with this, barrel length notwithstanding. Longer barrels can use slower powders too, and it's the relationship between case volume and bore volume that affects propellant selection for a given bullet weight IMO.
Add to this the effect of twist rate and it becomes even more difficult to unravel: according to my reloading manual (which goes beyond just posting load data) experiments have been done in which the rate of twist becomes progressively faster toward the muzzle in an attempt to prolong the pressure curve, presumably by using centrifugal force to keep the bullet tight. Although these attempts were ultimately unsuccessful, it seems to me the idea behind propellant selection for a rifle is to keep the bullet tight for as long as possible, which is surprisingly difficult to achieve with a long rifle barrel - especially when you have small case volume and a slow twist.
Admittedly the .243 may not have such a problem with it's ample case volume, which may in part explain it's popularity.