please do note that,
ballnuts are filled with not equally created steels balls(the ones that are all steel).
i heard of manufacturers using smaller balls as spacers in between all the slightly large balls to reduce friction when the run against eachother and this is an aspect to wreckon with if you want to end up with a smooth ballscrew.
i neer heared about plastic balls but it does stroke with spacing the actual loadbearingballs cause i can imagine what happen when they run against eachother.
so lots o measuring and read lots of nccam's post's for lots o info and lots of luck to ya!
Finally CHIPS you can have as much as you can without the doc. complainting about your cholesterol.