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Reloading 101: Pressure Curves and Port Pressure
When the bullet is sealing the bore, a longer barrel means more pressure is contained for a longer time. The smaller or larger the gas port size, the slower or faster the gas enters the system. The farther back or forward the port is located, the sooner or later. Bullet weight is a factor also: heavier bullets accelerate more slowly (This is also the reason heavy bullets erode the chamber throat faster than lighter bullets). Read the full story to understand pressure curves and port pressures.