What's the typical amount of backlash for a rolled ballscrew with a single nut and with a double nut?

I recently acquired a Jet Vertical mill and was quite impressed that the acme lead screws consistently have 0.004" of backlash... just a hair more than some of the rolled ballscrews that advertise 0.003-.004". The knee has just about zero backlash, maybe 5 tenths. I'm thinking about doing a simple 2-axis CNC conversion on this thing, mainly to eliminate the need for a DRO and power feeds.