Onager questions.

[Flavivs Aetivs]

The Payne-Galleway Onager design is a commonly perpetuated misconception, you are wasting so much energy by stopping the arm short like that. This is what a real Onager looked like:



The reason for the angled stop (in actuality they used a mound of dirt), is that way when the rock is released from the arm at the top of the swing it has the maximum amount of energy transferred into the stone.

And yes, they were known to splinter stonework but could not actually tear down fortifications. The Traction Trebuchet is what it took to do that, which didn't come about until the late 6th century and wasn't very accurate.

D.B. Campbell could tell you more.