The bullet is the
300g Nosler Partition.
The plywood sandwich was added to the front of the jugs, and knowing from past experience that the Nosler is a deep penetrating bullet, an extra jug was added to the back. The load was 80g Blackhorn, short black Harvester sabot, W209 primer. Range was 25 yard.
The first jug, and the fourth jug remained on the horse after all was done. The first and second jugs were shredded by the Nosler; it seems strange the first jug was able to remain seated. The bullet went through the five water jugs, and into the Laundry jug, where it stayed.
The photo shows the actual 'partition' between the front, and back of the bullet, that John designed, and tested back in the Nineteen hundreds. John started manufacture, and selling his design in 1948, did he not?