Using Williams' values for energy needed for bullets to penetrate, the 18kJ of a 0.50 BMG will penetrate about 12mm of mild steel plate, at normal incidence (the anti-armour sabot rounds will go through about 20mm of steel armour).

Given that brasses tend to be softer than mild steel, perhaps 19mm of brass (for non-sabot)? 2 inches might take about 80kJ.

An arrow will need less energy. But I don't think even the best Turkish archer could deliver 13kJ to the target.

(To be fair to Bacon, he did try to do experimental science once - but, alas, it killed him.)

Williams data is for round shot which has very poor penetration and ballistic performance due to the shape. Modern bullets have an entierly diffrent shape and performance.

Excellent. Thanks Glen.

i always relate these types of discussions to what i know about modern ballistics; esp when things like 'blunt trauma' are mentioned and how a non-penetrating hit from an arrow could supposedly knock someone down or daze them so much that they are vulnerable.

this video is from an incident in Iraq in 2005. a soldier was shot by a sniper using a 7.62x54R armor piercing round. his plate stopped the round and he was immediately able to recover and respond. i have estimated that when the round hit, it had 3434J of energy (184 grain round, impact velocity approx 2490 fps, 2532.9 foot pounds of energy).

http://youtu.be/c-UNFSZ8VKU


the plate was the original SAPI plate (not AP rated) over kevlar soft armor

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note that when he is shot, he impact spins him and when he falls, he falls straight down and is not knocked back. this imo, is more a reaction to realizing he's been shot than to the force of the bullet impacting.

examples like this lead me to believe that blunt trauma from a non-penetrating arrow with <200J of energy on plate could be shrugged off without too much effort

I always wondered why the arrow was so much hyped in the english speaking historical community. I looked up M. Junkelmann, Die Reiter Roms III again and he gives tha maximal force for a crouched lance thrust under ideal conditions with a 600 kg horse at a gallop of 40km/h at 186326.35 Newton/cm².
So the point of the crouched lance impacts with a lot more energy then a longbow arrow or crossbow bolt even at point blanc, I believe
And this is something (parts of) plate armour (and the man inside) was able to widthstand somehow.

Yeah, there's no question the couched lance hit harder than the arrow. You have various reports of lances penetrating mail and coats of plates both front and back. Humphrey Barwick invoked once such account to dismiss as useless the various lighter armors Sir John Smythe advocated. He noted such armors - specifically brigandines - might do well enough against arrows but had no place on a modern battlefield.

Marcos,

The issue is it is not that simple. I know people that have been knocked out after being hit by a bullet, though saved by their armour. A Cousin of mine is a cop and was hit and luckily he had his jacket on and it stopped the bullet but knocked him over and broke several ribs.

So while these stories are interesting and good to see the armour is saving the lives of our soldiers and friends every one represents a number of different events and factors.

I imagine though the US military does have some facts on this though.

RPM

this video is an excellent example of the effects of a projectile hitting hard armor. yes its old (1986) but it is fairly well known in the firearms community as it dispels the notion of a bullet knocking a man down...

http://youtu.be/aaS_2l8nGdg


the round used is 7.62x51mm NATO ball with 3414 J of energy...many times that which an arrow at any range will have

Exactly what I thought too, Clifford!
Of course, Dan is right, these numbers are far from those which would occur in a real lance impact. Yet the impact still would involve more force then an arrow.
So why do I read so often such unrealistic claims made in connection with the longbow? I mean men being unhorsed or toppled over by the impact, or beaten senseless in their armour?

I am on the armourside of the argument with Dan (as that arrows can penetrate armour sometimes, but do not have a significant effect on the outcome of an encounter by the direct deaths or heavy wounds the inflict but by other more indirect means), as long as we do not see a test made with a range of breastplates, helmets and limbarmour of different historical correct qualities (with the correct materials and thicknesses) mounted on the right foundation (aketon and maybe mail), and from a number of plausible distances shot with a number of plausible bow weights.
Also I would really like to see how a padded jupon like the one from Charles VI. (de France) would change the game- after reading the Jack test topic from Micheal Edelson, I think it will reduce the effect an arrow can have on the armoured man even more.