Originally Posted by JR TACTICAL
Why would the carbine run longer when dirty? is it because there is more gas being directed to the gas key in the shorter system?
Winner winner chicken dinner.
What makes the carbine batter the bolt/bolt-carrier harder and increases the recoil impulse also CAN add to reliability. However, running a bolt carrier group with one of the newer, advanced coatings to reduce friction can take back any 'reliability losses' (whether real or imagined) that may have been lost by the lower gas port pressure. Coatings from Fail Zero, ION Bond, and hard chrome greatly add to any carbine's reliability.
However, I think it would be important to add that 20" rifles, the 'most reliable' iteration of the AR platform, have only about HALF of the gas port pressure of a 16" M4 carbine w/ carbine gas system.
It's a balance between port pressure and dwell time (determined by the length of barrel between the gas port and the muzzle). I'm not sure of the perfect balance, but midlength 14.5" and 16" carbines are darn close to the 20" barreled rifle-gas-system ideal. Sleep well at night with your middy.