Lightfield suggests sighting in an inch or two (would have to read it again) high at 50 yards and this will put you on at 100 yards. Like said above it will really depend on your gun and the load you pick. Depending on how high your scope is, or if you use one it will effect the trajectory to some extent, as will the speed and weight of the bullet you use.

They suggest sighting in at 50 yards because for slug guns wind will not effect the bullet at 50 yards like it would at 100. I sort of agree with this, but I would still shoot it at 100 to verify the slug actually goes where you want it.

I like to start at 25 yards to make sure the gun is relatively close and the mounts don't need any adjustments then I move to 50 yards. At 50 I will set my windage and put my elevation where I think it should be. Then I move to 100 yards and touch it up. If it is calm out I will touch up my windage if it needs it and set my zero exactly were I want it. Then if I plan on shooting at farther distances I will shoot the gun at those ranges just to see where the slug really lands as opposed to where a chart says it should land.

I like to zero my guns at the distance I actually want them zeroed at, like my muzzle loader is zeroed for 130 yards, my slug gun was zeroed for 100 yards and my rifle will be zeroed at 200 yards. They get zeroed at those exact distances measured with the laser range finder I use to hunt with.

Paul