Forstner bits. I've only used them on drill presses though, never on a hand drill, but I suppose it could work..
Steelex D1024 3" Forstner Bit, 3'' https://www.amazon.com/dp/B0000DD0KZ/ref=cm_sw_r_apan_i_2TKK15N4EXDQFMARFVHC
It was probably a large forstner bit, or a lancelot blade
Edit: added links