Quote Originally Posted by Khisanth Magus
Actually, you may be suprised by the effectiveness of crossbows on plate armor. It was possible for a crossbow to reach a draw force of 350 lbf, which was enough to penetrate even plate mail when hit straight on. A glancing blow would, of course, just be deflected away.
We tried it with a 500 lbs. crossbow and a 80 lbs. longbow against a replica of a plate breast harness (original dated about 1480). Distance ca. 20 metres because of security and to avoid the strong flexing of the arrows during the first metres that hamper penetration. The plate has a thickness of between 2 (most parts) and 3 mm, which was a norm.

Total failure of the longbow which was capable to punch through 1,5 mm plate (as it was used for limb defences) but not 2 mm even if it hit straight on with 90 degree.

The crossbow bolts sometimes made holes in 2 mm plate but often did not penetrate enough to kill or severely injure the wearer (straw in that case)

Of cause, mail was no match at all for both weapons. Small, weak plate segments as in jacks may also not been the best defence but considering the enormous price of such replicas testing was not an option.

There were crossbows with pull weights up to 1000 lbs. and longbows up to 160 lbs. but presumably that was not the norm. (I cannot even shoot with a 80 lbs. bow )

By the way, bullets of an arquebus replica, dated about 1490, easily punched holes in 3 mm plates. It is not difficult to explain why that clumsy slow weapons soon replaced crossbows and bows. That arquebus was fired from the shoulder as it has a trigger. Such triggers appeared in greater numbers around 1500 and helped much to increase its use, unfortunately for the soldiers because of the terrible wounds guns inflicted and still inflict. Scientific progress is always wonderful.