P2K is a good range to zero a rifle at 100 yds. For an extra $5 you can get a lane with a video monitor so you can get instant feedback on your shots without a spotting scope and since it's indoor you don't have to worry about wind.
The downfall is that cease fire at the bottom of every hour to change targets so make sure you get a target that has multiple smaller targets on them. I prefer these for sighting in @ 100 yds as you can shoot multiple groups before each cease fire:
The downfall is that cease fire at the bottom of every hour to change targets so make sure you get a target that has multiple smaller targets on them. I prefer these for sighting in @ 100 yds as you can shoot multiple groups before each cease fire:

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