Quote Originally Posted by Renegade04 View Post
For several years, I was not on board with the mid-length thing. To me, being old school, a carbine had a carbine gas system. Well, about 7 years ago, did my first build with a mid-length gas system barrel. I do not know why it took me so long. Now, that does not mean that I am opposed to carbine gas system barrels. I certainly have my share of ARs with them. I also have my share of ARs with mid-length gas system barrels. The nice thing about these barrels is that they do run a bit smoother. I can still use a standard carbine buffer assembly (tube, spring, and buffer) and still have a smooth shooting AR. I have an 18" barrel with a mid-length gas system coupled with a BCM A5 Intermediate Buffer System and it is super smooth. I also did a build with a 14.5" mid-length barrel and coupled it with a standard carbine buffer assembly. It was so smooth that the first time I shot it, I could not tell that it cycled the next round. Would I trade up from an AR with a carbine gas system barrel to one with a mid-length gas system barrel? Only if I had a spare AR carbine laying around and I have done this. It was not to get a mid-length gas system barrel, but that particular weapon in general.

All in all, I would recommend building or buying an AR with a mid-length gas system barrel. You will immediately feel the difference.
For 18" I'd go with rifle gas system rather than midlength. Given that midlength works well on a 14.5" barrel, going to an 18" barrel is a big jump.