Have you ever thought about what really happens when the trigger is pulled? Well the following is a succession of events that occur when you let your finger press on the trigger enough to break the hammer free.



First, the firing pin strikes the primer causing the primer to be deformed on the bottom to the point where the anvil (the pointed part of the primer) crushes the primer compound causing it to ignite.

This ignition causes sparks to be blown through the flash hole in the bottom of the case, which in turn ignites the powder in the case.

The powder burns quickly creating large quantities of gas pressure inside the case. This pressure peak is what you will find listed in the powder and bullet loading manuals under C.U.P which stands for copper units of pressure, or PSI which stands for pounds per square inch. Each is a form of measureing the amount of pressure generated in the initial moments of ignition.

This pressure can rise to tens of thousands of pounds per square inch almost instantly.

The gas pressure expanding in the case presses against all the inner surfaces of the case and causes things to move in the direction away from the ignition source.

As the pressure increases the case expands against the chamber walls until it is held at that dimension and the pressure now can act on the bullet sitting in the mouth of the case.

As the bullet starts to move it builds speed until it hits the lands of the barrel. It needs to have some room to start moving before contacting the lands or the pressures may climb to high and cause a rupture of the case and damage may result to the gun and the shooter. Check out the page on excessive pressure for more information on pressure signs.

As the bullet travels into the barrel the gas pressure keeps pushing it forward and the walls of the barrel are pressing it in from the sides causing it to take on the shape of the barrel. The barrel rifling is twisted and it causes the bullet to spin as it travels down the length of the barrel. This twisting imparts a spin on the bullet which helps to keep it on target as it flies from the muzzle, toward its target.

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