My story is set in a fantasy Age of Sail. For the most part, anything magically made/ enchanted is quite expensive compared to the non-magical version.

This all to ask, in a sailing ship of forty guns, with a captain who is not extremely wealthy, would using spherical stones as ammunition for practice make sense? I am aware that very early cannons irl used lead-coated stones but I don't know if more 'modern' cannons would be able to use such things? Strengthening stones with magic is on the table here, which is why I mentioned above.

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    $\begingroup$ If you can manipulate the physical properties of the stones with magic, then what prevents you from just making them functionally identical to iron? That would immediately solve your problem, plus remove the need to ever use iron cannonballs when magic is available. $\endgroup$ Commented Aug 12, 2022 at 18:19
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    $\begingroup$ Iron is very much heavier than stone. The density of cast iron is about 7.2, the density of most ordinary stone is about 2.8. A ball of stone of the same size as a 32-pound ball of iron (very common for an age of sail demi-cannon) would weigh only 12 pounds; the two projectiles would behave in very very different ways when shot from the same cannon. (And the gunners would find that handling iron cannon balls in battle is an entirely different exercise, after practicing with lightweight stone balls.) (Plus I don't see why stone balls would be any cheaper. Making a stone ball is a lot of work.) $\endgroup$
    – AlexP
    Commented Aug 12, 2022 at 19:29
  • $\begingroup$ Consider why are they practicing 1. they are training to to load and fire quickly in which case there is no reason to waste balls, there may not even be a reason to fire the cannon. 2. they are practicing aim in which case you want to use the exact same ammunition you will be using in combat. $\endgroup$
    – John
    Commented Aug 14, 2022 at 2:02

2 Answers 2


Depends on the era. Stones were used for cannon until the wages for skilled stonecutters made iron balls more economical. That changeover happened between medieval times and the classic age of sail/piracy.

What would matter is shaping stones with magic, but even so it might be a bad idea to train with different ammunition than they use to fight.

Unless the training is not training the gunlayers, but rather the crew drill. In that case, actually firing the piece might give better results than simply loading it and running it out, only to unload it again. But to twist it again, what is the price of gunpowder? Does it limit the training even if stones are affordable?

  • $\begingroup$ A different and very much lighter ammunition. A cast iron ball is 2.5 times as heavy as a stone ball of the same size. $\endgroup$
    – AlexP
    Commented Aug 12, 2022 at 19:31

I don't know the relative cost of normal vs. magic, so I'm just going to comment on the practical aspects.

There are numerous problems with using stone balls as practice in the place of cast iron balls. The first is that, if your world has the technology required to make a cannon, then cannon balls are actually cheaper / easier to produce than spherical stones.

The second is that stone is much lighter than iron, by about half. This will make stone balls significantly less accurate. For an identical charge, they would have a greater muzzle velocity, but then be pushed around more by the air. They would slow down and drop earlier, too. You could use them to teach people how to use a cannon, but they'd be near worthless for target practice.

The third problem is that stones fracture. Some of this can be avoided by application of wadding, but there's nothing that will prevent the rock from fracturing on impact. Iron cannonballs can be recast, but stone ones are just broken.

Fourth, and probably most significant, is that stones that are hard enough to resist shattering from the initial explosion will probably be hard enough to scratch up the inside of the barrel. This would eventually result in the destruction of the cannon.

So, overall, it's a bad idea.

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    $\begingroup$ In the age of sail, "accurate" and "naval cannon" were not to be used in the same sentence. The caliber of the cannon was about 10% larger than the diameter of the balls, for starters. And the cannon had no, none, aiming devices. Engagements took place at distances of about 200 meters or most often less than that. There was no hope of scoring a hit on a ship a quarter of a mile away, except by sheer luck. (And the idea of re-using cannon balls fired at sea is funny,) $\endgroup$
    – AlexP
    Commented Aug 12, 2022 at 19:41
  • $\begingroup$ @AlexP, then what is there left to practice? $\endgroup$ Commented Aug 12, 2022 at 20:05
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    $\begingroup$ "What is there left to practice?" (1) Rate of fire. Rate of fire was the alpha and omega of naval engagements. (2) Firing in the general direction of the enemy ship, as opposed to into the sky or into the sea. This was really tricky; ships roll. It took a lot of practice to time the shot so that the cannon ball flew more or less horizontally. $\endgroup$
    – AlexP
    Commented Aug 12, 2022 at 20:07
  • $\begingroup$ @AlexP, (1) reloading drills are never live-fire. (2) You think the timing component of aim is greater than the wind-resistance drift of aim. I disagree, but can't think of a way of testing that conjecture, or looking up an answer, so I give up. $\endgroup$ Commented Aug 12, 2022 at 23:55

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