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In a nutshell: A tightbore inner barrel will increase accuracy over stock barrels. Heavier bbs will increase accuracy over lighter bbs. The TK Twist barrel has serious effective limits and should only be considered for low-powered (under 330 fps) AEGs. There seems to be a correlation between smaller bore diameter and increased accuracy.
I assume you are talking about fluting?They tried that, but it didnt turn out as good as they hoped. A sphere dosent have a defined axis of rotation, so when it exits it can go any way it wants. Sacrificing the lift gained from hop-up for rotaional stability is a poor exchange on a sphere in airsoft.