Originally Posted by
Common Soldier
64.5 kg would be close to the value of a Chinese picul, sometimes also called a stone, I think, so I wonder if HackneyScribe mistranslated as 64.5 lbs when it should have been kg. But then, the draw force would be unrealistically high for Chinese crossbows, at least hand held ones. Perhaps the rating of the crossbow mechanisms, which is what they were tested to, was not the rating of the actual crossbows. In engineering, you often use a safety factor of 2 when using equipment, so the device you are using is capabable of handling twice the actual load you expect to see. The crossbow mechanisms may have been tested to much higher loads than what the actual draw weight of the ceossbow. A 790 lbs ,rating of the mechanism becomes a more realistic 395 lbs draw weight.
And, since we don't have the stock and prod to go with the actual crossbow mechanisms, some of these crossbow mechanisms might have been for the much larger triplle crossbows and other siege crossbows, which did use mechanical windlasses.