significantly greater before bullet movement begins; equally, more granules will have ignited (more time will have elapsed since primer ignition).
Simultaneously, as shearing develops to create this plug, line-of-sight ignition occurs along plug perimeter and along interior of trapped cylinder. This significantly increases total area of surface burning, compared to the 45-70 (where the entire mass simply accelerates into the bore, while burning only along the rearward face).
Recoil is a Function of Mass and Acceleration
Rate
It is demonstrated that, at least initially, in the 45-70 a considerable
amount of propellant accelerates into the bore behind the bullet.
In a typical loading, this could amount to about 30 grains. Conversely,
in the 308, the propellant plug would contain about 10 grains. Equally,
energy consumed by accelerating solid propellant cannot contribute
to bullet acceleration; hence, case designs that accelerate less solid
propellant into the bore accelerate bullets more efficiently.
An understanding of the above will help one realize why case design matters. For example, consider a very fat and very short 30-caliber bottlenecked case. No such case is readily available but we could certainly create a case that held just as much propellant as the 308 Winchester but with a propellant column only about one-half inch long. In such a cartridge, primer ignition will reach the bullet base. In this instance, as pressure becomes sufficient to dislodge the bullet, no