Yes, 100 yard zero. Then shot longer distances with the cross-hairs on the aim point. Then I looked at how far below the aim point the group was. For my load, the BDC lines corresponded to 140yd and 175yd.

Like I said, there is some error in my drop numbers since I had one 3-shot group at each distance. I recorded 1.5" drop between 140 and 150 but 1" between 150 and 160. With more shooting, those number would be more accurate. A chronograph would be handy but it is always on the nice but not necessary list.