Chinese Crossbow History of Song Dynasty

This is my reproduction of a 11th century Song Dynasty Military Crossbow from China.
These were feared by the Mongols due to its effectiveness against Mongolian lamellar armor and shields.

The primary difference of these middle age weapons compared to ancient crossbows from China is the addition of the stirrup and a shorter powerstroke on average (based on archeological finds and artwork). We have more written evidence of horn prods in the Song Dynasty unlike ancient crossbows with scarce written proof of horn prods.

Modern firearm features like the trigger, the sear, the tumbler, the trigger guard, the sights, and the "pistol grip" are ancient inventions and revived in Song Dynasty China.

Sources:
From contemporary literature the Song era Divine Crossbow variant imply like it has a powerstroke of around 13-14 inches based on string length: In 1068, the Deputy Capital Commander Zhang Ruoshui and Commissioner of the Western Upper military district, Li Ping, were first summoned to consider and improve upon the simple-prod crossbow. Zhang Ruoshui came up with a new design for the crossbow and it was recommended by Li Hong and was actually a [new] variety of crossbow. The stock was made of mulberry and the prods of sandalwood. It had a stirrup made of iron and the arrow channel and latch were made of the bronze used to make spearheads. The string was hemp wound with silk. The stock was three [Chinese] feet and two inches (1 m) in length and the length of the string was two feet five inches (78 cm). The arrows were wood with fletching and a few inches long. It could penetrate a log of elm up to half an arrow-length fired from a distance of over 340 paces. - Song Shi, translation from Stephen Selby

From the Song source Cui Wei Xian Sheng Bei Zheng Lu:
──跷镫弩：牙里一尺八寸五分，葫芦头四寸，木檐长五尺八寸
Qiao Deng crossbow: Within teeth 1 chi 8 cun 5 fen. Gourd head 4 cun. Wooden prod 5 chi 8 cun.
──神臂弩：桩牙里一尺八寸，葫芦头四寸，镫二尺，桩长二尺三寸，角檐长四尺五寸。
Divine Arm crossbow: Within stock teeth 1 chi 8 cun, gourd head 4 cun, stirrup 2 chi, stock length 2 chi 3 cun. Horn prod length 4 chi 5 cun
──锹头弩：桩二尺，葫芦头五寸，镫五寸，山口五寸，锹头五寸，桩凡长四尺，木檐长七尺。
An artillery crossbow


Also

"If the prod is longer than 6 chi and if the stock is longer than 3 chi(38.8 inches), then at the shoulder the crossbow prod will tip toward the ground, and below there is the problem of tripping, when stepping on such a crossbow the stock head will reach the chest, so above there is no pulling strength…… At present day we want to use crossbows with draw strength of 2 stone to 3 stone (~264 lbs to ~397 lbs)…… The crossbow prod should be 5 chi(1.6 meters) to 6 chi(1.9 meters), and cannot be too long, so that short soldiers can easily shoot it at the shoulder. "
(Cui Wei Xain Sheng Bei Zheng Lu)

They were expected to shoot and then probably either retreat behind rows and rows of infantry at the last moment, or have the infantry behind them advance forward to protect them:
See Goose File formation from the Wujingzongyao with crossbowmen and archers shown at the very front

Special thanks to HackneyedScribe for the help with research and guidance

0:00 Intro
0:20 Components
2:20 History
9:35 Zoomed in
11:04 Testing outside