Scorch,Visible Impacts,Marbs,or anything with a thick shell and a fairly high grade
-Picky about paint
-Not the greatest accuracy
I have used this barrel for a total use of 1 playing day and several tests. I have very quickly learned that barrel does break paint more than some others, but that is expected due to the coarse inside of the barrel to give the ball its backspin. However, this can be prevented with the right paint. I suggest trying several paints before giving up on this barrel like I almost did. DON'T MAKE THIS MISTAKE! Just try something with a thick shell. Scorches worked best for me. Also, dont expect this barrel to have the best accuracy. It's built for distance with moderate accuracy when tuned and using the correct paint. I would recommend it for someone with a position like that of a heavy gunner, or for use of suppression.
My conclusion about the flatline is that it is a great barrel if used properly. Most can deal with the accuracy but SNIPERS BEWARE! Just look a little more into it before taking the plunge. But could you put a price on the ultimate heavy gunner barrel.