For those who are interested - here's a close-up of some of the ringing. Of possible interest is some explanation that this can happen during the period when the circuit is ostensibly open. The clue is in the negative triggering at the gate.
I'll be including that explanation in my report.
YELLOW TRACE CHANNEL 1 SHUNT @ 0.25 Ohm
PINK TRACE CHANNEL 2 BATTERY
BLUE TRACE GATE OF MOSFET IRFPG50