Plumbata

[ambrosius]

That sounds way too complicated.

Well, it isn't really. After all, Peter Connolly's experiments of throwing
the various types of pila show that there was also a considerable range
of weights for these, too. In fact, I think there was a similar range of
weights to your plumbatae, with the lightest pila being around o.5 kilos
and the heaviest (Renieblas) almost 2 kilos. With the lightest having the
longest ranges, and the heaviest the shortest. We don't even know how
the pila were thrown. Did only the front ranks throw? Did they throw
and rotate with the ones behind to maintain a constant barage (in some
situations)? Did a depth of six ranks all throw together, using the same
weight of pilum? Did six ranks throw together, but with a range of weights
to their pila, so that they all landed at the same range? And the same
questions could be asked for plumbatae.

We know from Arrian's formation to counter the Alans that he ordered
the front ranks to use their weapons (pila/spears?) as pikes, to halt the
cavalry charge, while the ranks behind indeed did throw their pila over
the heads of the front ranks. Maybe the same tactics were used for
plumbatae. If you want a depth of six or eight ranks all to throw at once
for maximum firepower, the you might want them to have different
weights of plumbatae so as to converge at a particular range.

Sure, you can vary the range by varying the trajectory, but as we all
know, 'mortar shots' can scare your own side as much as the enemy :o

As Mithras & Aitor point out, overarm gives more predictability (without
necessarily compromising the range). Maybe in combat what you might sometimes want is a uniform motion from all ranks with varying weights to give variation in the ranges. The truth is, we don't even know if the
Romans used over/underarm or both.

So when we're talking about big difference in weight, I personally would guess that it had to do with the amount of lead spent at the time, which may not have been properely measured before it was poored.

Sure, there would be some variation. But a mould should give you a
reasonably reproducible weight of lead each time. If there's a difference
of between 38 and 180+ grams then these were obviously made from
different sized moulds. Different moulds for differnent ranges? Of course,
maybe not all these weights would be in use at the same time, since
pilum weights varied through history. Maybe plumbatae weights might
have increased or decreased over time.

Ambrosius