I (Think) I have one of these units and I cannot see how the DTI is used to measure OAL. It would not contact the ogive so would be iffy at best, particularly with different bullet types. In the kit there is a dummy bullet and some sort of gaugue that measures the dummy bullet, but I have always used a stony point OAL gaugue with a machined cartridge or soem other method, then either a Stony point or better still a Shooting shed OAL or Bump gaugue on a vernier caliper.
For example, if I use case head to meplat on a 77Gr SMK HPBT or a 75Gr PPU HPBT, when I go to measure with a decent comparator there is a 0.030" difference, although in terms of actual length or mag length they are identical.
Godo job the AR15 dont care