Low Tech cannons mortars and shells
 

Good afternoon guys.

Looking into low tech, we see cannons, bombards and bombs.

But cannon and bombard ammo are solid rounds. There were no explosive shells prior to late TL5? I remember the pom-pom shooting black powder shells.

People before that did not have explosive rounds?

Saw in YouTube a brittish doc about bombards and the guys showed a castle wall that they've Said It was destroyed by bombard bombs.

Low tech give us the iron bomb. I assume people shot similar Shells?

Re: Low Tech cannons mortars and shells
 

I think GURPS Low Tech skips black powder shells because they are not really relevant to adventure stories. They tended to be fired by larger guns which required many men and animals to move and operate them, and they did not have enough penetrating power or an impact fuse to use in naval battles. On the rare times they come up you can use the shell fragment rules from the Basic Set.

For representative stats of the shells and hand grenades which were common in Europe by the 17th century see GURPS High Tech pp. 138, 190

Re: Low Tech cannons mortars and shells
 

IIRC from reading The Gunpowder Age, the Song and Jin dynasties were using catapults to hurl iron bombs at each other in the 1100s before guns were even invented. (Invention of guns had to wait for development of gunpowder with a higher proportion of nitrates.[1])

It doesn't seem impossible that someone could have created an explosive cannon shell long before TL 5, even without access to impact shells (edit: I mean impact fuses). That doesn't mean they did in Earth's history (I have no idea) but if you want to introduce one during your game, it's not inappropriate.

-Max

[1] From The Gunpowder Age: China, Military Innovation, and the Rise of the West in World History, Chapter 2:

How well did those recipes [from 1044 A.D.] work? A team of Chinese scholars used them to make batches of gunpowder, and although it’s extraordinarily difficult to reconstruct past practices from written records, what they learned is significant.

...Third, and most important, they found that these mixtures worked effectively only in the open air. When placed in sealed containers or in tubes, they burned slowly and incompletely. Gunpowder is so volatile because its nitrates supply oxygen, allowing rapid combustion, but these early recipes had low concentrations of nitrates relative to later formulas. The fact that these early gunpowder compounds required externally supplied oxygen to deflagrate effectively is an important finding.

Since early gunpowder formulas were unreactive and difficult to ignite, they wouldn’t have seemed suitable for guns or flamethrowers or bombs. This fact, not Confucian scholars’ supposed reluctance to take advantage of new technologies, explains why the Chinese didn’t immediately start making guns and bombs.

Re: Low Tech cannons mortars and shells
 

Looking at Wikipedia, it looks explosive shells are TL 4, but explosive shells that reasonably reliably explode where you want them to explode doesn't happen before TL 5.

Re: Low Tech cannons mortars and shells
 

A bit of online searching indicates explosive cannon shells date to the 14th century, or late TL 3; apparently the earliest ones were cast from bronze. They were typically used by mortars* rather than the longer cannons, and had a lot of issues - they could get jammed, explode prematurely, fail to explode, etc, and you had to light them prior to shooting them out of the mortar. For simplicity, I'd probably just use the LE guidelines from High Tech, using the Malf typical of TL 3 (or TL 4, if later - or just use TL 4 stats outright, and assume the first ones that showed up were just a case of TL 4 gear showing up a bit early). Actually, given they were notoriously finicky, I'd probably apply a -1 to Malf, both for the mortar firing it and for the shell itself (they aren't as reliable as typical iron bombs). Or maybe have that first -1 only apply to cannons, with the shorter-barreled mortars not having much issue launching them.

*I honestly can't recall of mortars actually show up in LT - it might have only been longer cannon. ISTR at least one of the ridiculously-large weapons in LTC2 making a note that it would technically qualify as a mortar (the barrel was only a few calibers long, but it was one heck of a caliber), but I don't remember more appropriately-sized mortars actually being in LT.

Re: Low Tech cannons mortars and shells
 

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).

Re: Low Tech cannons mortars and shells
 

The definitions of 'mortar', 'cannon', 'gun', 'howitzer', and their hybrids are fairly arbitrary and differ from one country to another, and have differed over time as well. For TL3-5 using 'mortar' to mean 'an artillery piece that fires on a high arc, allowing indirect fire' and 'cannon' or 'gun' to refer to everything that doesn't do this is generally going to be fine if you're not trying to distinguish further.

Re: Low Tech cannons mortars and shells
 

Its also generally harder to research early incendiary and low-explosive projectiles than solid shot. You can't just take shot mass, bore diameter, estimate muzzle velocity and call it good, and the tests are more dangerous.

GURPS Low Tech: Medieval China could be a fun supplement.

Re: Low Tech cannons mortars and shells
 

You also have the problem that they don't leave very good artifacts for later archeologists. A shell that exploded isn't going to tell you much. A shell that failed to explode as designed might still explode later, or someone might remove it because it's a hazard. If none of those happens... plants think gunpowder is fertilizer, and an iron shell case isn't exactly the most weatherproof of components either.

Re: Low Tech cannons mortars and shells
 

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