Who made the barrel, what material is it? Is there a coating on it? How is the finish, glass smooth with the refraction test or can you see machining marks?
I have seen Action "6.03mm" barrels with a horrendous finish on them. You could see scratches and a spiral, which says they pulled it off the mill to fast and then didn't finish the surface after the initial bore...it short horribly...
LAMBDA ONE 420mm Steel 6.01 Precision Barrel for AEG Replicas
Highest-quality precision barrel with a diameter of 6.01 mm made of SUS304 stainless steel in Japan. Barrels by LAMBDA are manufactured using very precise CNC machines as well as manually finished and individually tested