Originally Posted by ADAIR
Also, powder capacity is not everything. Take a look at 300Win Mag vs. 300WSM. Some cartridges are more efficient.
If you read recent articles in various mags, this case capacity effeciency thing is a myth and more quality marketing then internal ballistic fact.
When both cases are loaded to the same charge density, pressures and effective barrel lengths, the larger 300WM will go faster in every single bullet weight.
More fuel, more thrust, more obvious the heavier the bullet.
Most factory loads are no where near maximized with lots of room in the case.
This extra case volume was not gone unnoticed and smaller cartridges designed to get closer to 100% load density became a way at showing effeciency.
With the multitude of powders, MOST cases can be run to their fullest potential.
And when you get there....
There is no replacement for displacement.
I shoot a 6.5 Mystic or a 260AI (pretty much the same thing) and push 140gr Berger VLD's just over 2900fps in my F class rigs.
Most 6.5X284 shooters also reach similar velocities but use a case quite a bit larger and burn more powder. They however, load a low density powder which doesn't max the case volume but keeps the bullet in the accuracy node.
So they use a bit more powder to get the same speeds. Not effecient at all.
If they were able to load to the next velocity node, THEN the extra case volume would be of value.
However, accuracy is not always as good so the case is under utlized and yes, INEFFECIENT.
If someone came out with a 'tween powder that would take advantage of the case volume, I bet we will see all 6.5X284s screaming into the 3100fps range leaving the smaller cases in their dust.