I usually sight in using the same set up I use for benchrest shooting, front and rear sandbags (bulls bag front bag). Occasionally I'll use one of my adjustable front rests from my 1,000yrd rifles, but usually, the sandbag is plenty stable.

For sighting in at 100yrds, I usually mount the scope and use a laser bore sighter at 50yrds, then take ONE shot at 25 to make sure it's on target. I usually want it somewhere between dead-on to 1" high at 25yrds. If it's more than 1" in any direction from that line, I'll adjust and take one more shot. (2" off at 25yrds is 8" at 100yrds, so that much error might be off the page at 100yrds). All I care about at 25yrds is that I'll be on the target PAGE at 100yrds. I don't fine tune at 25, and then RE-TUNE at 100.

I then move to 100yrds and take a 3 shot group. I make the necessary corrections and take a 5 shot group. If the first 3 of the 5 shot group aren't dead-on (using spotting scope), then I'll adjust after 3, and fire another 5 shot group.

So typically, I use 9 shots to sight in any given rifle.