There really is no flair at the end of the gas tube. Take a good look and mic one up. I have two sitting here in front of me, I think they are from dpms. The tube diameter is .180 the tip that looks like it has a flair is .180 also. What makes it look like a flair is that two inch long section that is only .168. that starts about 3/16 from the end. My guess is that its there to reduce drag on the bolt carrier key as it moves. What I did on my 7 inch barrel with the short gas tube was cut down a rifle length gas tube to the length I needed ( I added a 1/8 inch allowing for the tube to shrink from the bends I needed to put in it). I cut this from the gas block side, this gave me a nice straight tube to start with. I put it in my drill press, supported the free end with a nail and a clamp for support and I ran a file on the tube giving me that 2 inch .168 section on the chamber side about 1/8 inch from the end. I then bent the tube by holding it in a vice and gently tapping it with a hammer. The hardest thing was bending it to the angles I needed. Here is my barrel with the gas tube I made, the gas block is open on both ends. Its not that hard you can do it