You're using whatever target you choose in centerfire classes.
3. All target entries shall be 3 groups of 5(3 rounds for HS classes) rounds each, and the average group size, shot consecutively at 100yds for all Center fire, and 50yds for all Rimfire. Modification for 2015 and later: Center fire groups may be shot at ranges beyond 100 yards. Measure the actual group sizes in inches and report the group sizes and the range at which the groups were shot to the moderator, who will compute an effective group size at 100 yards. (Group sizes shot at 200 yards will be divided by 2, etc.)