Polished internals allow for smoother cycling of the internal moving parts, also it can help lenghten the life of your O-rings as well. (smoother surface vs rough surfaces).



As far as polishing too much, you don't need to worry about that so much as people seem to think sometimes. The rear bolt only needs to make an air-tight seal in the rear of the powertube so that the blowback stage forces the bolt out of the power tube for the next cycle.

If you look at the receiver halves before polishing you will notcie then that there is not an air-tight seal such as with the rear portion of the powertube.

Like others said, just make sure the surface is nice and smooth, glossy look is good, but just don't spend too much time on them so that the bolt starts to rattle around from side to side.

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