"As far as I've been able to determine (and I'll say it yet again), the end of effective burning is signalled by the pressure peak."
Is ALL of the powder that is going to burn burned at the at the pressure peak?
The reason I ask, as the bullet accelerates down the barrel,the bore volume is increasing, resulting in a corresponding drop in pressure.
If the bullet is out running the pressure build up of powder continuing to burn, would not that also result in the pressure drop.
I remember reading that for the M1 Garand, a powder in the burning rate range of IMR 4895 is recommended over a slower powder such as IMR 4350. The reason given is that the pressure, with IMR 4350, at the gas port opening, is too high and can cause damage to the gas operated mechanism, where the pressure from the smaller amount and faster burning rate of IMR 4895 has dropped low enough to prevent damage to the operating rod.
This would indicate to me that a larger amount of slower burning powder remains at a higher pressure, even after the peak has been reached, for the entire length of the barrel.
The peak would not necessarily be higher or last for a longer interval, but the drop in pressure on down the barrel would not decrease as much.
