How is the bullet propelled through the barrel after firing a rifle?

The bullet is propelled through the barrel after firing a rifle primarily due to the expanding gases produced when the gunpowder ignites. When a cartridge is fired, the primer is struck, igniting the gunpowder within the cartridge. This combustion generates a rapid expansion of gas, which creates high pressure in the sealed chamber of the barrel.

As the gas expands, it pushes against the base of the bullet, driving it forward through the rifled barrel, where the spiral grooves impart spin for improved accuracy. The critical factor here is the pressure from the expanding gases, which is what provides the force needed to propel the bullet out of the barrel and towards its target.

Other processes involved, such as the primer explosion and the action of the firing pin, are preliminary steps that set off the sequence leading to the bullet's propulsion but do not directly drive the bullet through the barrel itself. The piece that stands out as the main mechanism for propelling the bullet is indeed the expanding gas.