Schramm mystery ballista???

[Koyuncu]

According to Ancient Engineers' Inventions;

Since we have a detailed description from Philon of Byzantium, we know that the construction of this weapon began with the forming of bronze leaves or folios (foils), which he called scales. Numerous allusions indicate that Ctesibius’ bronze springs only had two layers. The first secured to the opposing symmetrical layer by means of two pins, the second secured to the extrados of both, leaving the ends free.

Book's Reconstruction of Springs;



I have no idea how they got the information about number of springs but if this is the case then you may be right about lack of evidence about leaf springs.