Gas Tubes

A: 14.5" barrels can be either a carbine or mid-length gas operating lengths. To see if you need a carbine or mid-length gas tube measure from upper receiver to the gas block shoulder of the barrel if it's carbine length it will measure about 7" and if mid-length it will measure about 9". If you have just the barrel you can measure from the front of the barrel extension to the gas block shoulder and it will be 6 3/4" for carbine and 8 3/4" for mid-length.