solid propellant plug will follow the bullet into the bore. All else being equal, accelerating mass will be minimized.
This means that the gun will initially accelerate more slowly into the shooter's shoulder – less felt recoil; less total work will be done on the barrel – less barrel heating and wear; and more work will be done on the bullet – more velocity! Any shooter who has done a side-by-side comparison of otherwise nominally identical guns chambered in 300 Win Mag and 300 WSM, will agree that the shorter case generates less felt recoil, despite essentially identical ballistics. This is explained by the fact that the 300 WSM accelerates far less unburned propellant into the bore. (We are not breaking Newton's law here, total recoil may be similar but the initial rearward gun acceleration will be milder and that is what the shooter is most sensitive to.)
Hence, in general, when considering identical usable case capacities, bottlenecked cases are vastly more efficient than cylindrical cases and progressively shorter bottlenecked cases are progressively more efficient. Modern designs are simply getting closer to the ideal, where the case body is sufficiently short so that very little unignited propellant follows bullet into bore.
Barrel Life Considerations
A complication exists regarding
barrel life. Consider the 243 Win and 6mm Rem. The 243 has about 4%
less usable case capacity. It also works at a slightly lower pressure.
Shoulder angle is