Low Tech cannons mortars and shells

[Rupert]

Explosive shells were fired from mortars, which date from early 15th century Korea and had reached Europe by the mid-15th century. That'd make mortars a TL4 invention. However, at that time they were firing stone balls, though shells did come into use soon afterwards.

As for why nobody used shell in cannons, there are a few reasons. Firstly, until the early 18th century (TL5), the fuses were lit by hand and then the gun fired, and doing this with a long barrel cannon wasn't practical. Secondly, cannons were a lot more powerful than mortars and had a non-zero chance of detonating the shell's charge upon firing. Thirdly, the fuses time-setting was terrible, and that meant with a cannon that the shell was probably nowhere near the target when it went off, but with a mortar firing on a very high arc the shell wouldn't move far from its impact point.

Now, all of these things were solved over time - it was found that fuses would ignite from the flash of firing even if the shell was placed fuse-forward in the gun (the other way round and the flash might get into the shell and set it off instantly), but this was a TL5 discovery. Making this work in a cannon required a wooden sabot to hold the shell during ramming and firing (which also help cushion the impact of firing), another TL5 invention. Better powders made the shells less likely to blow up when they shouldn't - also TL5 and even TL6.

However, that still left the unreliable timing of the fuse, and that wasn't solved until late TL5 and into TL6 (and even TL7), and unlike all the previous innovations this is not something you can back-port to TL4 (though making decent quantities of TL5 gunpowder probably requires that you uplift some parts of the place's industry to TL5 anyway).

[stranger38]

Originally Posted by Rupert

Explosive shells were fired from mortars, which date from early 15th century Korea and had reached Europe by the mid-15th century. That'd make mortars a TL4 invention. However, at that time they were firing stone balls, though shells did come into use soon afterwards.

As for why nobody used shell in cannons, there are a few reasons. Firstly, until the early 18th century (TL5), the fuses were lit by hand and then the gun fired, and doing this with a long barrel cannon wasn't practical. Secondly, cannons were a lot more powerful than mortars and had a non-zero chance of detonating the shell's charge upon firing. Thirdly, the fuses time-setting was terrible, and that meant with a cannon that the shell was probably nowhere near the target when it went off, but with a mortar firing on a very high arc the shell wouldn't move far from its impact point.

Now, all of these things were solved over time - it was found that fuses would ignite from the flash of firing even if the shell was placed fuse-forward in the gun (the other way round and the flash might get into the shell and set it off instantly), but this was a TL5 discovery. Making this work in a cannon required a wooden sabot to hold the shell during ramming and firing (which also help cushion the impact of firing), another TL5 invention. Better powders made the shells less likely to blow up when they shouldn't - also TL5 and even TL6.

However, that still left the unreliable timing of the fuse, and that wasn't solved until late TL5 and into TL6 (and even TL7), and unlike all the previous innovations this is not something you can back-port to TL4 (though making decent quantities of TL5 gunpowder probably requires that you uplift some parts of the place's industry to TL5 anyway).

So, short answer is yes, and long answer is "they kinda use them"

[Fred Brackin]

Originally Posted by stranger38

So, short answer is yes, and long answer is "they kinda use them"

You need to add in a "but they didn't work very well at all.".Or even an "They were more dangerous to the users than the targets".

[Pursuivant]

Originally Posted by Fred Brackin

You need to add in a "but they didn't work very well at all.".Or even an "They were more dangerous to the users than the targets".

By the 18th century, they were sufficiently reliable and effective that they were part of every artilleryman's arsenal.

You can use the HT stats for a black powder grenade as a basis for a 1 lb. shell.

After that, assume a hollow sphere with 0.375 to 1-inch thick walls depending on shell size and the rest of the volume is black powder. Model volume of powder as 4/3 PI r^3 where R is (shot diameter - (wall thickness x 2))/2. Assuming a density of 50 lbs/ft^3 for black powder you can work out explosive damage based on weight

There is general information about black powder artillery shells in GURPS 3E High Tech 3rd Edition. It says that BP shells do explosive damage based on filler weight, which is usually about 10% of total shell weight. Fragmentation damage is 2d to 12d+ cutting damage per hex within the fragmentation radius. Material picked up from a ground burst material might add 1d-4 to 1d-2 HP cutting.

I consider the GURPS 3E HT rules for shrapnel to be remarkably generous. Unless they were specifically shrapnel shells (shell filled with musket balls) cast-iron shells tended to shatter into just a few pieces. Air bursts directed shrapnel in all directions rather than just towards the ground like modern shrapnel shells. Ground bursts buried themselves in the ground so shrapnel fragments just got buried in the earth or channeled upwards with the blast.

That's not to say they weren't potentially lethal, just not "instant wound/death" as the rules imply. In particular, fuze-timing was a huge issue for pre-20th c. shells, so shells might burst before they reached the target or after they'd passed it by/buried themselves in the ground.

Battlefield archeologists/scavengers regularly collect shell fragments from the ACW and other 19th c. conflicts, which gives you a sense of relative lack of fragmentation damage.

As a SWAG, I'd suggest 1d HP pi++ damage for a low-explosive driven lead ball, 2d cut for a chunk of cast iron shell, with chance of a hit (3d) being 12 for shrapnel, 9 for shells) with normal penalties for range to hit more distant targets. A critical hit means a hit by some sort of shrapnel out to ~2x normal blast radius.

Way too much information on late 19th c. artillery here.

[Polydamas]

Originally Posted by Pursuivant

By the 18th century, they were sufficiently reliable and effective that they were part of every artilleryman's arsenal.

I don't think that the average three- or four-pounder-crew or naval gun crew had explosive shells in the 18th century (which GURPS calls TL 5). Instead, a well-equipped European artillery park would have some weapons with explosive shells.

As late as the Napoleonic Wars, Wikipedia suggests that the only French field guns with a shell were the 6" howitzers https://en.wikipedia.org/wiki/Obusie...ces_Gribeauval https://en.wikipedia.org/wiki/Gribeauval_system (they also had mortars for sieges)

[Pursuivant]

Originally Posted by Polydamas

I don't think that the average three- or four-pounder-crew or naval gun crew had explosive shells in the 18th century (which GURPS calls TL 5). Instead, a well-equipped European artillery park would have some weapons with explosive shells.

You're right. Shells were specialist weapons until the early 19th century, when Henry Shrapnel's invention was adopted by the British Army. Even then, they were tricky to use due to fuze timing problems and only really came into their own with improvements in fuzing and shell design in the 1850s.

Pre-19th century shells were mostly used as counterbattery and siege ordnance. I believe that they were mostly used by large guns, as you describe, since the ratio of powder to shell volume improves with shell diameter, making them a more useful weapon. Swivel gun or "galloper gun" light cannons probably wouldn't have used shells.

That said, the grenades of the era were spherical, cast iron and probably tough enough to survive being shot out of a cannon. I don't have any evidence for it, but I can't believe that artillerymen never experimented with the idea.* Shooting cast-iron grenades out of a Coehorn-style mortar would be a way to make them useful as a siege or countersiege weapon.

*

 In pre-20th century armies, artillery and engineering officers were the inventors and intellectuals, which is why top-ranked West Point graduates went into those arms. Infantry officers were a mixed lot, and cavalry officers had a reputation for aggression and lack of book smarts. (E.g., a joke from the British Raj, "Did you hear about the new cavalry lieutenant?" "No? He was so stupid the others noticed!")

[Polydamas]

Hand mortars were a thing (with no stats in GURPS Low Tech!) https://en.wikipedia.org/wiki/Hand_mortar but as long as the fuse had to be lit by hand there were practical problems shooting shell from a long-barrelled, small-bore gun.

Early gunpowder artillery is really complicated and could easily be a booklet by itself. Even GURPS High Tech has one gun (!) to represent all traditional muzzle-loading cannon of the 18th and 19th centuries.

[Rupert]

Originally Posted by Pursuivant

By the 18th century, they were sufficiently reliable and effective that they were part of every artilleryman's arsenal.

And that's early-mid TL5, and they were still not the standard for guns, but a speciality round.

[Anthony]

Late TL 5 they became pretty standard, but that's 19th century, not 18th.

[Dalillama]

Apparently there were explosive musket bullets in the mid-19th century, which saw some use in the ACW. The St. Petersburg Declaration of 1868 barred the Great Powers from using explosive rounds smaller that 400g/1 lb, a prohibition later ratified by the Hague Conventions, which drew more signatories. Presumably this is part of why there aren't many examples of explosive ammunition for small arms.