AR-15 Gastubes
Direct Gas Impingement
The AR15 uses direct gas pressure to move the valve backward, for different barrel lengths there are also different lengths of gas tubes:
Pistol Length 6 3/4 inches - 17.1 cm
Carbine Length 9 3/4 inches - 24.7 cm
Mid Length= 11 3/4 inches - 29.8 cm
Rifle Length = 15 1/4 inches - 38.7 cm
What length gas tube do you need?
Not sure what size you need? Measure the distance from the shoulder of the barrel to the gas port on your barrel and compare to the table below. (carbine is the most common length).
Distance to gas port:
Gun length = 4 inches / 10.1 cm
Carbine length = 7 inches / 17.8 cm
Mid-length = 9 inches / 22.9 cm
Rifle length = 12 inches / 30.5 cm