Discussion came up in the $1k arsenal comments around the reliability of carbine-length gas systems on AR-15s. Wanted to share a couple good reads on the subject:
AR-15 Buyer's Guide at the New Rifleman (good overall guide, scroll down for the gas-system discussion)
"Even though the carbine has an “aggressive” gas system, it is still a reliable machine. It may experience parts breakage sooner in its life than the other configurations, but we’re talking many thousands of rounds before that *might* occur."
And another good 'un:
Carbine vs. Mid-length on 16" Barrels
My thoughts: A carbine-gassed 16" should still run plenty reliably, just harder on the parts and with a bit more recoil impulse. My personal AR-15 has been a carbine-gassed 16" gun for years and has run 100% with mostly Wolf/Tula crap ammo run through it. If you have the choice, I'd go with a mid-length on a 16" barrel, but I wouldn't loose much sleep over it if you can't.