A simple measuring method is place the buttplate flat on the floor, move the gun to a wall thats 90degress to the floor and have the fences touch the wall. Measure the distance from the wall to the muzzle. Bingo!!. FWIW, O-2" is for bunny hunting, 2-3" for upland, above 3" for New Years, July 4th celebrations and for the gun you loan your brother in law. Now go figure. Randy


RMC