Onager - range/size/load

[Crispianus]

Larger onager over 300 metres

Thanks again! I see that in his comments on the siege tower of Demetrius Poliorcetes, Vitruvius writes that it was intended to 'withstand the blow of a stone weighing three hundred and sixty pounds shot from a ballista' - this implies that 360lbs was the maximum weight of shot. Is Vitruvius generally held to be reliable in his measurements?

If so, and if we could assume that the largest sort of single-armed onager could throw a missile of the same weight as the largest sort of twin-armed ballista (and if not, why switch to an inferior weapon?), then it does seem that this sort of weight of shot would be feasible - and perhaps over 300 metres too.

Would a single-armed onager allow a higher trajectory shot from its sling than a stone-throwing ballista, perhaps? If so, then we could be looking at an even greater range.

I think the comments regarding the Heliopolis seems unlikely to me and obviously it was never tested, the solution to it was much simpler in the end, the defenders created an artificial bog (litterally) in front of the wall it was in position to attack and it simply bogged down... I assume though that it would have been rendered proof against red hot bolts etc.
360Ibs is indeed the maximum size Vitruvius gives and think this is consistant with other authors, I would assume this is the maximum practical size for such a machine, it may be that beyond this the machine would be less effective rather then more or simply impractical, the deciding limit seems to be the size of the torsion element..

The ranges given previously are all from "modern"experimental machines, the actual ranges given in antiguity are much more up to 800m for smaller machines, but not as far as I'm aware 360Ib'er, these would probably have a range of no more then 300m(or less) and in a siege may have had to be as close as 150m to attack a wall effectively... which brings its own problems...

Josephus claims Vespasians one talent machines were firing from around 400m+ and were very effective at clearing the walls of defenders, creating a veritable storm of shot... which would suggest that their actual max range was a great deal more..

Maximum range is not the whole answer though every weapon has an absolute maximum and effective max range, accuracy may be the deciding factor and this is likely to be variable at best... so a shorter range may well have been prefered...

Maybe where the Onager scores is ease of manufacture and use, I could imagine that a Ballista with its double torsion element would be more difficult to build and tune... quit apart from that it might be that the single (longer?) arm of the Onager is more efficient.

Personally I think the Gun/howitzer-Ballista/Onager thing is a red herring as both could be used to produce the same result, it should be noted that torsion machines were used during WW1 for lobbing grenades in trench warfare.