@I am ELCUPRA: In this video, it’s about how to choose an inner barrel to upgrade your Airsoft gun. The inner barrel has various width levels. It depends on your style. The 6 mm. round bullet is a common standard of Airsoft guns and inner barrel, has a width of 6.05 +++ so it can be used with various grades of 6 mm. world wild. If you want to upgrade the inner barrel to 6.01 / 6.02 it will give you more accuracy. The 6.03 / 6.04 / 6.05 +++ inner barrel will boost the distance more far but less accuracy than above.