Like the alto flute, there is no standard bore size for the bass flute, and each maker has developed their own approach to the instrument's scale, including subtle differences to key positioning and size, as well as the size of the bore and the shape of the headjoint's embouchure hole.
Generally speaking, the wider the instrument's bore, the richer the tone in the low register is. However, a big bore requires more air from the player, can have a slower response time, and may also result in a weaker high register. Different bore sizes may also alter the reponse and balance of some multiphonics. The choice of bore is a personal decision for each player, and should be based on the main use for the instrument. For example, a large bore instrument with a strong low register would be ideal for flute choir playing, whereas a virtuoso soloist may be better suited to a small more instrument for greater flexibility across the range and a faster response.