The Tangent Boat-tail 2 projectile is the same as the Aberdeen Proving Ground G5 projectile, which remained a reference projectile for the US Ordnance until 1960.
This projectile has a shorter boat tail and a slightly blunter nose than the TBT projectile listed, and is similar in shape to many of the hunting and game bullets made by all the bullet manufacturers, hence the reason for its inclusion. For such bullets, this would be the standard projectile shape of choice.
Second order polynomial functions were fitted to the drag data to create the drag functions used in the program. They are listed below: