Superb! Replaced the stock brass barrel in my Cyma CM.132s which I believe is around 6.05mm. The CM.132s shoots around 210fps out of the box and has reasonable accuracy. I upgraded mine to an M75 spring which took it to 250fps but threw the accuracy off. The Lambda 6.01mm inner barrel has made it much more accurate and increased FPS to 270. I did have to carefully slice/file the ridge from my hop rubber as the groove in the Lambda barrel is on the opposite side but this hasn't caused any issues so far.