There are LOTS of valid comments in this discussion.
I'm a cop, and currently my duty gun is a Sig 226R-DAK in .40 cal. (A department transition to the Glock 22 after the beginning of the NEXT fiscal year (July 2013) is being evaluated).
My department DOES NOT issue practice ammo on any regular basis.
I shoot 250 rnds a month through my duty gun. Usually in one practice session.
I find right around 200 rnds to be a good amount for a single practice session when shooting centerfire guns -- sometimes if I'm shooting a .22 I'll shoot more than that, up to 250 or 300.
(I buy commercial .40 cal reloads from my local commercial reloader, or Ultramax reloads from Sportsman's Guide, or "Canned Heat" reloads from Georgia Arms.)
I have a whole bunch of different practice courses I use, depending upon what I'm trying to practice, how much time I have, am I on an indoor range or outdoor range, how busy the range is, etc. As one of the others in this discussion has noted, many ranges have some limitations on what you're allowed to do for safety reasons. Just do whatever you can and don't worry about it.
Practice on basic skills with a focus on timely accuracy is ALWAYS a good idea.
You can only learn from experience if you pay attention!