StreamOfTheSky
Adventurer
The crossbow could be specialized refit, a repeating crossbow with a crank, a la the Chinese Repeating Crossbow. According to the website, "By means of this arrangement one hundred men could discharge two thousand arrows in fifteen seconds." Dividing the total number of arrows by the total number of men, nets 20 arrows per 15 seconds per person. Cutting that roughly in half, 9 bolts in 6 seconds is entirely reasonable.
Yes, repeating corssbows are amazing, I'm surprised no one else brought it up. On the other hand...didn't those have considerable reload time? I don't dispute being able ot bombard an enemy with bolts in any one round, people in real life could do that, as you show. But to be able to repeat that round after round?