Yes, momentum is a much better way of gauging penetration than KE. Unfortunately KE is just so popular that all the arrow against armour tests I have seen are measured in terms of Joules/Newton Meters. I just didn't want to confuse everything by throwing around Newtons when everything I've stated up to this point is in terms of Joules. Although one of the funnier things with bows is that you usually get a KE boost when you increase the weight of the arrow (that’s not the reason why I suggested heavier bolts for the heavier crossbow though). By increasing the weight of the projectile you are increasing the efficiency of the system (bow and arrow), these tests kind of illustrate the effect.

http://www.atarn.org/islamic/akarpowicz/turkish_bow_tests.htm

Also David, technically, the only way the energy of your crossbows is being represented in your bolts is in the velocity they are imparted with, it can't manifest itself in any other meaningful way. How the bolt retains its velocity is decided first and foremost by its shape and initial velocity.

This test illustrates some of the mechanics involved in bow and arrow efficiency... its kind of a hard read though :eek:

http://www.bio.vu.nl/thb/users/kooi/kobe97.pdf

David;

There is no magic involved in the sense that the bolt would know that the crossbow it is being shot from is a 100 at 1000 or even a 10000 pounds of draw: Now heavier prod, everything else being equal, should give you more power unless all the power is being wasted just moving itself :eek: If it's giving a heavy but slow " push " all that energy is not doing anything if it is not moving your bolt faster unless you are using a heavier bolt.

O.K. I'm repeating myself here. ;)

Big IFF: If you have a 4 oz bolt moving at 200 ft/sec shot from one crossbow and a 4 oz bolt at 200 ft/sec at the same 200 ft/sec using a crossbow with a draw 3X the first one, you have exactly the same amount of Ke / momentum. Oh, and a very heavy crossbow whose limb are not moving the string any faster.

Since I think you seem to be getting more out of the heavy crossbow using the same bolts at the same weight: Then your bolt has to be moving faster for you to get any different results. My best guess would be that your measuring of bolt speed is giving you erroneous numbers.

Though if you can double the weight of bolt with an insignificant loss of velocity you would be almost doubling the amount of Momentum. Like you said in a very early post: With no bolt on the crossbow the speed of the bow string will be at it's maximum, adding a bolt will slow down the string by a very small amount but even a much heavier bolt might mean only loosing a few ft/sec of velocity. The ideal crossbow bolt is the one giving you the most amount of momentum even at the cost of some speed. At some point increasing the bolt weight hits the point of diminishing returns where the lost off velocity will be great enough that your bolt will loose speed AND momentum.

I don't have to have any special knowledge of crossbows function, it's just external ballistics that counts: The internal ballistics deals with the efficiency of the launching system.

Anyone out there with a degree in physics please feel free to correct any mistakes I may have made in my argument or something I have not taken into consideration.

I would also suggest using a heavier bodkin which has a cross section as large as the shaft, thereby allowing the shaft to more easily follow into the hole made by the head, rather than whittling down the diameter of the shaft body behind the bodkin.
The tip of a best quality bodkin should have steel forged into the body of wrought iron.
Mark Stretton's recent work indicates that there is no advantage in having a loose fit to the shaft when shooting at a hard target.
The shock of impact has even caused a shaft to open up the socket and come free, so reducing the mass at a crucial moment.
A loose fitting barbed head might be effective on a soft target, but it seems more practical to make the shafts to a consistent standard since you would not want the inconvenience of sorting through shafts in the heat of battle.
Rod.

David,
Email me rod@englishlongbowevents.com and I will send you illustrations of various types.
Rod.

I have been doing a limited amount of preliminary shooting at padding and it occurs to me that careful attention will need to be paid to the shape of the bodkin.
Whilst a short nosed heavy bodkin might be effective against plate, punching a hole which the shaft can then follow on through, where there is strong thick padding on top of maille a short nosed head may well have too great a compressing effect on the padding.
Conventional wisdom names the long needle bodkin as a specific against maille, but more importantly in my view, it seems to be the type which is best at piercing thick padding and long enough to both pierce padding efficiently and long enough to also find an aperture in the maille beneath.
It will be worth comparing the performance of the long needle, the small bodkin, the large bodkin and the small type 16 barbed against heavy padding over maille.
Rod.

Jean,
I agree with you about increasing the weight of the crossbow bolt until the point is reached where performance falls off.
With bows the generally accepted guideline is 10 grains of shaft weight for every pound of draw weight.
This tallies with a 175 lb draw longbow shooting a 4 oz war shaft (1750 grains).
Applying the same rule to the crossbow, a 400 lb crossbow should be able to easily project a 9 oz bolt.
With the bow shooting a much lighter arrow can often leave unused energy in the limbs which can manifest itself to the archer as handshock and it is not uncommon to tame a slightly unpleasant shooting bow by using a heavier string and shaft.
Rod.

Now that's more like it :D You've pretty much equaled a 150lbs longbow with that 450lbs crossbow of yours. Also, by comparing the data you gave me on 150lbs composite crossbow to the results of a 136lbs composite bow it looks like you have almost equaled that as well :surprised: All in all it's very impressive.

David;

Thanks for that test as it does seem to confirm the theory that momentum of a heavy bolt at a moderate lost of velocity gives a lot of punch. I assume this is with a medium heavy crossbow you have been using in the 450 pound range ? With the even heavier 1200 pounder you are planning to make your velocity figures might be similar with an even heavier bolt.

Forgetting completely about period performance, we can still arrive at modern comparative tests of what maximizes bolt penetration in modern media. Anyway, my original title for this thread was power and range of crossbows ! And not just
" historical performance " . I'm interested in this topic to learn all I can about crossbows and not just period plate.

Obviously, tests that would correlate closely with period conditions are something to try to achieve but what we can say is that you have first hand physical evidence of what you shoot at and with what, we can each of us decide what we think it means, I hope !?

Oh, with those much heavier bolt close range power may mean a loss of potential range and a very " rainbow trajectory " at long range. For maximum range the ideal weight of bolt would probably be like your usual lighter ones.

You can get more range by going lighter but with a war shaft the lower weight limit is set by the lower threshold of energy required to still penetrate a protected target. You could use a flight shaft and go further but it would trouble no-one (suitably attired) when it arrived.
Lets see how 10 grains to the lb of draw weight penetrates and how it affects your fps.
Rod.

I wish that people who are doing these modern tests would simply stay within the context of what they are doing. I want to see the stopping of definitive statements of what was done historically, how things performed throughout history, etc. The simple fact is this: such definitive statements cannot be made by shooting a modern-made projectile from a modern-made weapon into a modern-made target without significant research, understanding, and effort to faithfully recreate materials, conditions, and constructional details.

So what? There is a lot of other things that can be learned from doing such tests, including knowing what possibly could have happened historically. It can't answer that question, but it can answer others. The tests will be interesting nonetheless.

All I ask is that people doing such testing stay within the context of the tests and stop making definitive conclusions without a proper scientific method. There is a lot of value to such tests. Why make them controversial by trying to make them something they are not?