On page 65 of the USMC TM 10698A-10/1 it states "it is recommended that the iron sights of the combat shotgun be zeroed at a range of 100 meters with a single projectile (slug) ammunition and 25 meters using multiple projectile (00 or 000 buckshot, etc.). It is also recommended that three-round groups be fired prior to making adjustments when zeroing with slugs.”