This article describes a simple method to make a cheiroballistra handle. The end result is functionally equivalent to Iriarte's interpretation of the handle, i.e. it locks the slider into a strong nail/pin after the weapon has been cocked. The main difference to Iriarte's handle is that the loop is round, instead of rectangular; this greatly simplifies the process of making the handle.
All this said, the cheiroballistra manuscripts clearly show that handle is rectangular and fairly wide. This could mean that the handle was actually used as a real handle to assist slider pullback and thus allow higher energy storage. This question is best answered through experimentation by testing if the cheiroballistra springs can store more energy than what can be generated with stomach pressure alone.
The process step by stepEdit
Take a length of thin (~3mm) steel bar and forge it into below shape; the loop is easiest to form around the hook of the anvil.
Next a drill small hole near the loop. A rivet is later forged into this hole to prevent the loop from opening up under pressure. Drill a larger hole near the end of the handle; this latter hole is used for the handle axle:
Insert the axle into the axle hole, and the rivet into the rivet hole:
Forge the rivet tight:
The handle is now ready to be attached into the slider.