Direct impingement

The jet of gas can blow debris away from the ejection port which, in other designs, could enter the mechanism and foul the gun.

The main disadvantage of direct impingement is that the breech of the firing mechanism becomes fouled more quickly compared to long or short stroke piston systems.

This is caused by the operating mechanism's direct exposure to gases from burned cartridge propellant when the firearm cycles.

The gases contain vaporized metals, carbon, and impurities in a gaseous state until they condense on the relatively cooler operating parts.

Both the French and Swedish rifles use a simple system whereby the gas tube acts as a piston with a cylinder recess in the bolt carrier.

The original AR-10 action designed by Eugene Stoner (later developed into the ArmaLite AR-15, M16 rifle, and M4 carbine) is commonly called a direct impingement system, but it does not actually utilize this mechanism.