I am building a 6 ARC upper and now I am looking for the barrel I would like. One of the questions I have is that some of the barrels I see are "+1" or "+2".

I assume this means +1 or 2 inches in length of the gas system. My question would be 'why'?

I understand when you go shorter you have to have a short enough gas system, that's pretty easy, but I don't quite understand the reasoning behind going longer that 'standard'. From a straight up functionality standpoint I am not sure what purpose or benefit these extra long gas systems serve.

The only thing I could even remotely think of is in relation to dwell time but I still haven't wrapped my head around the reasoning.