Well Max, we are really weary of the mundane, the expected, the usual, the typical, the predictable, the common and the ordinary. So we are going way way out on a limb and thinking maybe there is a chance that this was the result of an early ordnance inventor, perhaps stationed at the fort during the antebellum years. After all, successful Ring-Airfoil projectiles have been developed prior to WWI and anyone who has ever flown a kite knows what an airfoil looks like and increased range is one of the proven benefits of this type of round. Just because all of the ring airfoil projectiles have been rifled, doesn't mean that there cannot be some long ago experiments conducted to see if a smoothbore, using an aligning sabot, could accomplish the logical goal of increased range as well.
Of course it'd unlikely, but that does not mean impossible.
Food for thought,
Tracy and Mike
