well the mag power tube is already within .005"
I would not want to get it any tighter than .003" different metals expand at different rates, and you need some freedom of movement for speed. making the whole thing within too tight of tolerances would only add friction to the set-up, not what you want. grease would not be good for this either. you don't want that getting blown down the barrel and ruining accuracy.
I have a design to use some delrin rings(like palmer's design) that will hopefully seal like I want it to, and keep the friction as low as it can be.
the bolt doesn't move all the way out. the bolt stem barely does in stock form I believe.
I don't understand your idea of holes.
in my design (as of now), the bolt stem will be a bit larger most of it's length and will come completely out of the power tube tip about .030" the back of the bolt will still be riding on the power tube.the air will be released at a precise time and waste is minimized by the power tube tip outer seal, and the lack of the ever increasing opposing spring force that would nornally slow the bolt down and decrease the release time and flow area.
the bolt travel can be whatever you want ot make it, but .700" is just too small. it will be more like .900" when it's all said and done. the loss of air in the breech is more than the air that would be gained in the cylinder by making the stroke as short as .7"