Water basically weighs 1 gram per centimetre.
"not as effective as lead" is not the same as "more effective than iron".
"Effectiveness as projectiles" is somewhat vague given the context. Technically accurate but it can get caught up in things like penetration and stopping power. We only care about flight performance when it comes to brute-forcing through their wind-deflection.
Those responses seem uncertain to me due to the question marks. Also, I do not believe that discord is an official source of information on the game. Convenient, no doubt, but such thingsare best handled on the thread where everyone can see them and the full context.
so... I don't really want to have to deal with discord stuff... But the datapoints that I get are:
Lead is greater than crystal for "projectiles".
Crystal weighs an otherwise unknown value between one and one seventh as much as our current shells.
Lead is soft, which makes it good against soft targets, but poor at penetration. As a bullet it can be regarded as very bad for certain niche roles. Its flight characteristics, though, are superior to steel, as air will not deform lead at any sane velocity. As a "thing to project to a distance" it is good, but "projectile" can be inferred to mean "bullet"...
So crystals could weigh two times as much as water, and be one third as effective as our current shells. My feeling from the thread is that it is probably close to four or five times as much as water, but I really couldn't be certain. I believe that steel is slightly, well, less than 10%, heavier than iron, so it is not impossible that it is heavier than iron, but I cannot see that being borne out from the descriptions of it.
I do not know of any qualities that crystal has that would influence it's flight-path other than pure density. Crystals have fractal designs, which tend towards rough surfaces at a chemical scale. Metals tend to be smooth. It really isn't possible to say that one would have a more aerodynamic surface than the other, but the metal is probably easier to polish while the crystal is probably easier to forge smooth in the factory, so I guess it depends how gritty they get in transit? Crystals do grow under certain circumstances, so they might tend to stick together and deform if left adjacent to one another for a long time? But really, the surface is an unknown factor, but metal comes highly recommended as a projectile by all the world's armies, so it certainly isn't 'bad'. So all that we really have to go on is density? I mean, sure, other things come into play once you actually hit the thing, but right now we are incapable of attacking their long-ranged stuff as it is faster and longer ranged that anything that we have.
So the continued value of cannons, as derived from its ammunition, is a matter of density. And crystal is an unknown density in a range which includes densities less than a seventh of that of our current bullets.
We know already that our current bullets are not good enough due to their susceptibility to wind. We know that lead would be better. Revising crystal works to summon something more like lead, such as weightite, is confirmed as an upgrade, and would be a better revision given that range is our current problem. I did not notice any significant problems with rate-of-fire last turn.