OK I use a 50 yard zero for 90% of the shooting that I do with the .17HMR. With this zero I hit dead center of a 1" circle with every shot. Now using the same zero at 100 yards I hit the bottom of the same 1" circle. So for all practical purposes the 50 and 100 yards zeros are the same. If ,for instance, your target area is a 2" cirlce then you can run that same 50 yard zero to around 120 yards and you will not ever "fall" out of that 2" target zone. As far as how the impact will be as if you shoot at something in the 20 to 30 yard range then you will hit high by as much as the height of your scope. I will test this but I am sure that using the same 2" target zone you should still be placing shots inside of that area. Just keep in mind that the level of accuracy that you desire may require you to do some adjustments to your scope. For most small game hunting a 2" target zone is about right.
Thanks for the intrest in this post. I am sorry that I do not have any new data to add at this time. I was unable to make it to the range over the last few days. I do however plan on making it this weekend and will post the results here as soon as I decipher my notes..............CHEERS
Man, you need a good spotting scope
Also, if you're looking for decent targets on a budget, look at Wal-Mart for those wooden sign-posts (little "garage sale" style thin wooden slats that you put in your yard - they have adhesive on them), and some of those aluminum pans from the dollar store (or Wal-Mart).
You get the "ding" sound, as well as some visible holes to use and it costs about $2 a target (no worries about steel plates at that point).