Did a search and generally came up with minus 2.5 inches as an answer.

I want to get a 100 yard zero on a 6.8 SPC 16 inch upper, but only have access to a 25 yard indoor range to do it at.

Where should my POI versus POA be for a 100 yard zero? Ammo will be the Federal Fusion 115 grain SP most likely with potential for the Hornady 120 grain SST depending on what's available.

This will eventually be used as a shorter range hunting upper and shot placement will be critical for sake of the game.

Is the -2.5 accurate for the weight class?