I have recently learned about a peculiar type of projectile used by the Byzantines. It is a dart, about half an arrow's length, feathered, with a broadhead with a very long socket and an egg-shaped lead weight in the beggining of the socket. The whole weight, socket and head are equal to about 1/3rd of the whole length of the projecile. If we can prove that this is an efficient ammo for a cestrosphendone, that may lead to a conclussion on wheter they were used regularly by the Byzantines, for there are some quite a lot of short plumbata popping up in archaeological sites. Please, those with the skills and tools to build such test my theory. Here is a guide on making them: http://www.fectio.org.uk/articles/makeplumbata.htm