I built an 18 inch Mid Gas rifle with a Innovative Arms WAR Receiver. These receivers are meant to work with 5.56 barrel with a certain gas port size. So when you use a 6.5 G you introduce a variable that it isn't designed to work with. In my case there wasn't enough gas to make it work. I ended up drilling out the gas port to .1094, up from the original size of approximately .094. Now it works great and has been completely reliable, soft shooting and quiet but it did take some trial and error.
BTW I am using an Omega.
BTW I am using an Omega.