OSR: Meddling with Magic Cannons

In the previous post, I wrote up my rules for cannons and a class that uses them.

Cannons are rare in my games. They aren't mass produced. Each one is unique. Black powder is still uncommon. Handguns are just tiny cannons on sticks.

Anyone with the Cannoneer skill, 300gp in raw materials (iron, clay, wax, etc.), and access to a forge can make a cannon in 2 weeks. Limited tools, distractions, or modifications may add 1d4 weeks.

These rules are intended for replacement cannons. Cannoneers aren't sitting around churning out cannons because the startup costs are very high and there's no market without a trained crew. A cannon by itself is just a metal tube. A belligerent noble won't pay for the tube; they want a crew as well, ready for deployment to the latest war. And since no sensible noble would accept a novice cannoneer when the master is available...

Bad Decisions and Bad Alloys

So you've looted a tomb and filled your pockets and packs with magical treasures. Some of them are useful. Some of them... less so. Normally you'd sell the chaff in town for extra gold. But the Cannoneer in your group is eyeing that chainmail of lubricity with eager eyes. They've got a horrible, cunning plan.

Magical Cannons don't exist in my setting... yet. I know my players. They're going to be the first ones to make them. I'm going to be prepared.

Mixing Metals
As a general rule, most metals can be alloyed, but not all metals should be alloyed. Mix two incompatible metals and your cannon could turn green, fall apart, shatter, grow long spiny hairs, or rust into fragments in days. On the other hand, you could be completely fine. Metallurgy is a fiendishly complicated art.

There are only 2 types of cannons we need to worry about and a limited number of other metals.

Iron No
Iron Yes
Copper Yes
Copper No
Tin Yes
Tin No
Lead Yes
Lead No
Zinc Yes
Zinc Yes
Silver Yes
Silver No
Gold Yes
Gold No
Glass No
Glass Yes
Mercury No
Mercury No
Carbon No
Carbon Yes
Mithril Yes
Mithril No
Adamant No
Adamant Yes

Carbon in this case refers to anything organic (scrolls, wands, devoted followers, etc.)
Values for mithril and adamant are made up, obviously.

3 lb experimental gun. Caliber 80 x 230 mm; length 156 cm; weight 492 kg. Cast 1722 in Olonitz. Carriage 2nd half 18th century.

Casting Cannons

First, buy your raw ingredients, make your clay cannon mould, and heat your metal (bronze or iron). Once it's melted and as hot as you care to make it, add your spare magic items. Each time you add an item, roll on the table below. Add +1 to the roll for each magic item added previously. It's a good idea to put your most potent enchanted item in first and add minor items later.

1d10 Result
1-7 No Effect
8 Negation
9 Burp
10 Explosion

The item's enchantment does not survive the alloying process.

The item's enchantment triggers briefly. This could spoil the process, scatter metal everywhere, or do nothing of value. If you can't think of an effect, the item just spits out a blob of magical energy instead (1d6 damage, 30' radius, breaks windows, frightens neighbors, and sets dogs howling).

The item's enchantment detonates and releases its stored magical energy, enhanced and concentrated by the molten metal. [Level]d6 damage, [Level]x10' radius, Save for half, other effects based on the enchantment as needed. If total damage rolled is <10, the molten metal can still be recovered and used.

Proper Precautions
If the cannoneer takes suitable magical precautions, they may reroll on the table once per casting. Add rerolls if their precautions are particularly interesting. They should be mythic, illogical, or alchemical. Examples: heating the forge on dryad wood, using a witch's cauldron as the iron base metal, carving prayers into the forge's clay, etc. Say "yes" to anything they suggest. This is a new art; some things will work, others won't, but the players have no way of knowing.

The Result

Once the cannon is cast, roll to determine the cannon's quality. Add +1 per metal added that is incompatible (see the charts above).

1d10 Result
1 Brilliant. Cannon is harder and sturdier than expected. Reroll "Spiked" Misfire results.
2 Light. Cannon takes up 12 inventory slots instead of 14.
3 Blessed. Subtract -1 to any rolls on the Misfire table.
4 Sturdy. Any critical hits inflicted deal an extra 1d6 damage.
5 Beautiful. Cannon has a pleasant finish and an unusual colour.
6 Shiny. Cannon has a pleasant finish.
7 Lumpen. Cannon has an unusual finish.
8 Warped. Half range for all range brackets.
9 Cursed. Add +1 to any rolls on the Misfire table.
10 Brittle. Add +4 to any rolls on the Misfire table. 
11 Shoddy. Cannon collapses after 1d6 uses (as Spiked result)
12+ Disaster. Cannon rots and falls apart in hours.

E.g. Thormund cast a bronze cannon and added the toe of Vecna (carbon), a steel (iron) +1 helmet, and a silver ring of protection from creditors. He rolls on the table with a +2 bonus (from the iron in the steel helmet and the carbon in the toe of Vecna). The silver is compatible with bronze.
Hellcannon, GamesWorkshop

Things to Smelt

The effects of enchantments on a cannon will need to be adjudicated on a case-by-case basis. I tend to use unqiue magic items in my games. What happens when the PCs smelt:
- a gold ring that lets the bearer see smells
-an electrum plate that contains a lightning bolt spell
-a shrunken head that detects lies but also whispers your darkest secrets
-a half-invisible cat

I have no idea how I'd build a table that could possibly encompass these options. But I'm sure you can think of a few ways these materials could affect a cannon.

Weird synergies are ideal. Here are a few ideas.

+X Weapons and Armour: Generally make the cannon sturdier. +X to Attack and Damage.
Ring of Feather Fall. Cannon's weight and inventory slot requirements reduced. Recoil becomes slightly trickier to manage.
Ring of Elemental Resistance (fire). Reduced severity on the Misfire table.
Ring of Shooting Stars, Magic Missile, Fireball, etc. Spells have a chance of firing along with the cannon, or they add extra damage or range, or the cannon just explodes the first time it's used.

Stick them on the surface of the cannon instead of melting them down.

Rods and Staves
Mount them along the top of the cannon like a sight.

Put them inside cannonballs and add a fuse (if the scroll can be activated by burning it). Alternatively, toss it into the molten metal (as carbon).

Unholy Items
Classic demon horns, iron shackles, phylacteries, vampire teeth, soulsteel, etc. Can use holy water or relics as gunpowder.

Party Synergy
Elementalist Wizards can carve stone cannonballs into little curled-up  homonculi or biting faces, then convince them to attack on arrival. They could also pacify the fire elementals inside the cannon. Exorcists could carve warding runes into the cannonballs to let them strike ghosts, or somehow build a spectral cannonball that strikes the soul but ignores the flesh.

Johann Hartlieb's Kriegsbuch, 1411, Cod.vind. 3069, Austrian National Library Vienna

Bonus Table: Cannon Names

As suggested by G+, with some adaptations and real-life names.

1d50 Cannon Name
1 Wrath
2 River of Mercy
3 Miss Morningstar
4 The Password
5 Wicked Wind
6 Terminus 
7 The Belcher
8 Act of God
9 Judgement
10 Last Measure
11 Viper
12 Big Mean Bastard
13 Brunhild's Kiss
14 Armor Eater
15 Pickling's Shot
16 The Noisy Killer
17 Hullo There!
18 Madame Pepperpot
19 The Son of Ruin and Contempt
20 Kingfucker
21 Herald's Bane
22 Perforator
23 Huckleberry
24 The Last Word
25 Fever and Flame
26 Militant Mind
27 The Cudgel
28 Knightsbane
29 The Brass Kettle
30 Strong Drink
31 The Mule
32 Sufficient
33 A Fresh Plague
34 Armistice Wallace
35 Firebrand
36 All the King's Men
37 No Subtlety
38 Unseater
39 Sweet Dreams
40 Adder
41 Answer
42 In Wroth Adorned
43 Giant's Whisper
44 The Weeviler
45 Hunger
46 Hecate's Cauldron
47 Blue Brandisher
48 The Iron Hare
49 Creaking Old Otto
50 Sharp Fart


  1. Do you have thoughts on PCs making their own magic items? Would that look anything like this process?

    1. I'm working on a separate post for duplicating spells and enchanting items. But if you wanted to forge a magic hammer from a magic sword, and the enchantment was compatible, this type of system would make a great baseline. Alternatively, you could melt down all your magic rings into a magic breastplate (and probably explode).