90mm recoiless rifle round. High Explosive Anti Tank (HEAT). Don't know the nomenclature off the top of my head. I've fired one, though :grin:
Why does it have fins if it's fired from a 'rifled' gun, you ask? Spin reduces the effectiveness of the shaped charge warhead... so by fin stabilizing the round, instead of spin stabilizing, they get a little more horsepower out of the shaped charge. The driving band spins freely, so it does not impart any spin to the round.