It's basically a jackhammer
Thanks for this insight. I guess I was being somewhat flippant all around; an auger style tool would obviously be a significantly different design and would need something to work against (but then, the current mole seems to, too).
It's pretty ambitious to aim for 5m into soil of such unknown composition. Heck, we have enough trouble getting a clear run digging holes for planting trees around here.
Anyway, I wish it well!
Biting the hand that feeds IT
