How did the Chinese crossbows that shot bullets work?

Question

It's commonly accepted that East Asian people invented the crossbow. However, it seems they had crossbows that shoot bullets as well. As an example, Jing Fang uses this description when explaining his model of solar sustem and eclipses:

The moon and the planets are Yin; they have shape but no light. This they receive only when the sun illuminates them. The former masters regarded the sun as round like a crossbow bullet, and they thought the moon had the nature of a mirror. Some of them recognized the moon as a ball too. Those parts of the moon which the sun illuminates look bright, those parts which it does not, remain dark

I wonder if there's a graphical depiction or reconstruction of such mechanism. Could it be some sort of primitive rifle?

Additionally: Did western crossbows (since Roman Empire) evolve from Asian ones, or did they evolve from the gastraphetes? Roman crossbows are way more similar to Asian ones, but they were close to Greece and I didn't find anything about the Western x-bow evolution.

Answer 1

"Rifle" is a bit ill defined here. A rifle is:

a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves ("rifling") cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile (for small arms usage, called a bullet), imparting spin around an axis corresponding to the orientation of the weapon.

That would increase flight stability of bullets, but the fins do that on arrows and darts already.

What the Chinese had was at least a repeating crossbow:

The repeating crossbow (Chinese: 連弩; pinyin: Lián Nŭ), also known as the Zhuge crossbow (Chinese: 諸葛弩; pinyin: Zhūgé nǔ, previously romanized Chu-ko-nu) due to the design upgrade contributed by Three Kingdoms-era strategist Zhuge Liang (181—234 AD), is an ancient Chinese crossbow where the separate actions of stringing the bow, placing the bolt and shooting it can be accomplished with a simple one-handed movement while keeping the crossbow stationary. This allows a higher rate of fire than a normal crossbow: there is a top-mounted magazine containing a reservoir of bolts that are fed by gravity, and the mechanism is worked by simply moving a rectangular lever forward and backward.

A video of this in action is here.

Bullet shooting crossbows:

A bullet-shooting crossbow, sometimes referred to as “stone bow,” is a modified version of the classic crossbow. The bow was usually constructed with wood or steel, depending on the preference. It typically utilizes bullets and stones as projectiles instead of the traditional quarrel. […]
Flaws:
Many intended to use the bullet-shooting crossbow as a weapon, but it had its limitations. While the bow worked well on small animals like squirrels and birds, it was not powerful enough to be a reliable weapon in war. The velocity was just too low for the bullets or stone to pierce skin, and therefore it didn’t cause much damage to humans. The bullet-shooting crossbow had the potential to fracture skulls, but as this was the only effective way to take down the enemy, the bullet-shooting crossbow didn't match up with the standard crossbow in wartime.
In addition to the low-velocity shots of the bullet-shooting crossbow, the projectiles were not as effective as the bolt on the standard crossbow. The sharp bolts of the crossbow did more damage than the slow-moving, blunt bullets of the bullet-shooting crossbow. Because the standard bolt does more damage, the bullet-shooting crossbow was reserved for hunting smaller animals. There was no reason to use a bolt-shooting crossbow to hunt squirrels when a smaller, less-powerful weapon could get the job done just as effectively.
Another flaw lies in the material of choice: steel. Steel bows require more energy to return the bow to its original position and therefore deliver less energy to the shot itself. Bows made of wood typically shot much faster than those made of steel.

Answer 2

The Chinese bullet crossbow was more like a slingshot than a rifle (or usual crossbow). It fired hard objects such as stones, rather than sharp objects with metal points such as bolts or arrows. The "bullets" were first placed into pouches, which were fitted with springs. The "crossbow" itself used a double string mechanism. This fact, together with the pouch and spring arrangement made it much easier for the "average" person to shoot it than was the case with regular bows (which required highly skilled archers).

The bullet crossbow had much less force than a regular crossbow, which in turn had much less force than a rifle. None of the crossbows used gunpowder or other explosives that gave guns their force. But the bullet crossbow, which was designed for "amateurs" (e.g. for hunting birds or small animals), by design had less force than normal crossbows. A bullet crossbow could kill a human only with difficulty (e.g. a direct shot to the skull, like a slingshot).

Answer 3

Chinese crossbows that shot bullets or pellets (round stone or clay pellets) were primarily used for hunting small animals like birds and squirrels, and continued to be made until the 20th centuries, when they seem to have been banned by Mao as part of his crackdown on traditional Chinese culture. They seem to be used a lot like a sling shot, with the deflection of the prod, often made from a bamboo composite, providing the propulsive force instead of an elastic rubber band. These bullet crossbows often had sights on them.

These bullet style crossbows were also built in Europe, which often had a similar shape to the Chinese ones. But the European crossbow prods were typically steel and the ones from the 16th century used a horizontal lever trigger, as did other European crossbows. By the 19th century, European crossbows were using vertical trigger levers. The oldest physical examples I have seen of Chinese bullet crossbows dated from the 18th or 19th century. Like European crossbows, these Chinese pellet crossbows had short power strokes.

Bullet crossbows as well as using stone balls, could use clay balls or lead balls, which would be cheaper to make than regular crossbow bolts.

Here is an early 20th century Chinese pellet crossbow https://www.mandarinmansion.com/sites/default/files/2019-07/chinese-pellet-crossbow19.jpg

This is a 16th century European pellet crossbow https://www.metmuseum.org/art/collection/search/33746