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Jean Thibodeau




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PostPosted: Tue 16 May, 2006 12:35 pm    Post subject: Crossbows power / range         Reply with quote

Just been reading an interesting discussion on the range of crossbows on Netsword site.
http://netsword.com/ubb/Forum8/HTML/000234.html

Here is a link to a crossbow maker who made some very interesting comments towards the end of the Netsword topic thread:
Seem worth having a look, LINK REMOVED BY ADMINISTRATORS

Very interesting data on comparative power of goat foot crossbows and heavy siege crossbows.

Have a look and have a read of the above and them we can have some good discussions about power and range and maybe also get confused about the physics of the whole thing.

I would think that one can do all sorts of math about acceleration curves and length of draw but to me the only thing the arrow or bolt reacts to is the speed of string as it leaves the bow or crossbow: The arrow or bolt only moves as fast as the string was moving and if the acceleration was over a short or long distance the arrow doesn't care. Razz After it leave the string the arrow or bolt can only loose speed ! ( Unless one is shooting from a high place to a lower target. )

Oh, this one looks good: LINK REMOVED BY ADMINISTRATORS

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Jean Thibodeau




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PostPosted: Thu 18 May, 2006 9:02 am    Post subject:         Reply with quote

Oh, just one little bump up and if you read the linked topic there is some interesting info I will just give a few highlights of, info I haven't easily found elsewhere: The goat's foot crossbows having a draw weight of around 450 pounds, the cranequin around 750 pounds and some heavy siege crossbows 1200 / 1500 pounds.

There is a post about a crossbow being tested that was left cocked for 500 years and still having a draw weight of 1500 pounds with an " unproved to me " statement that it is estimated that the draw weight was originally around 3000 pounds.

Anyway, this is the information I found most interesting. Eek! Laughing Out Loud

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David Ruff




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PostPosted: Thu 18 May, 2006 10:29 am    Post subject:         Reply with quote

Thanks for the comments.

The 380/450lb goatsfoot bow is alive and strong. Currently for sale now too. Tis the problem with building crossbows. Build one - like it, sell it, rinse and repeat.

We are forging some 1200 to 1700lb prods at the forge and will be doing some windlass and crank bows soon, will start posting results on those when we get done Happy
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Jean Thibodeau




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PostPosted: Thu 18 May, 2006 2:37 pm    Post subject:         Reply with quote

David Ruff wrote:
Thanks for the comments.

The 380/450lb goatsfoot bow is alive and strong. Currently for sale now too. Tis the problem with building crossbows. Build one - like it, sell it, rinse and repeat.

We are forging some 1200 to 1700lb prods at the forge and will be doing some windlass and crank bows soon, will start posting results on those when we get done Happy




Welcome to this site. Big Grin I found your comments very informative on that other site that I thought it would be worth it to bring some attention to it. Information based on functional crossbows at these power level is not something I've run into before and a while back when I asked if anyone could tell us what the relative power levels of the different type of crossbows were, all I got was a lot of silence. Laughing Out Loud

I wonder also about the power level of crossbows using just a belt hook ? Maybe a lot more than one would assume ?

If using a belt hook I would adjust the length of the hook so as to just bend the knees as little needed to to just have the range of motion that straitening the knees would be equal to the length of draw. I believe that one would not bend over and pull with the lower back but one would stay vertical and just push with the legs.

I believe that very heavy weight of pull could be handled this way as long as the belt was wide so as to not cut into the waist. Since I can do 20 reps with a legs press pulley machine at 500 pounds, cocking a crossbow with basically the same movement as short range of motion squat, I think a 400 to 500 pound crossbow could be easily cocked ( If that is the right word ? ) this way.

With a goat's foot the main advantage would be able to cock a crossbow from different positions: Sitting, hiding behind cover and maybe on horseback. What is the leverage advantage using the goat's foot ? I would think it would vary during the cocking stroke between 4 to 10 because the leverage would change due to the curves in the lever ( My guess, )

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David Ruff




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PostPosted: Thu 18 May, 2006 9:01 pm    Post subject:         Reply with quote

Belt hooks are interesting things, They attahed via a ring to the stock below the trigger (for anyone whom is not familure with one) on a post like an "L" hook and then looped around the string (via a metal hook) and back up to a loop or hook that attached to the belt. This set up was a very effective - but crude - 50% let off.

In my belthooks i have cocked upto about 400lbs with moderate effort, i have maxed a 700lb bow, but let me tell you - just becuase you can "squat it" doesn't mean do it heheheh. You have to remember that you were gonna do this loading for awhile and it takes its toll on the back, legs and waist in a hurry.


Most medieval crossbows spanned only 4 to 6 inches, so the actual lift of the hook with the legs was very short and fast, Most modern target crossbows in medieval form pull 7 to 8", this is due to the low poundage - need to make power so a longer stroke is needed. In a high poundage you can use a short stroke with a lot of weight. Also they made prods that were hit and miss, so you didn't want to bend them a lot. Where now a days we can bend steel 8" of stroke and be safe doing it due to exacting specs in the steels we use.

It is true that it is easy to cock a belthook bow in the 400 to 500lb range, and people then were pretty stout and could handle it. However........

The belt hooks back then cocked from one side of the string, it made the bow off center, once you get the string cocked you could NOT move the string over to center it - so the cocking method was very inaccurate and no consistancy in it. Even modern day rope cockers (same thing as a belt hook) cock the bow off center, however even at the max power bows that are sold today you can center the string with a tug.

Belthooks were ONLY used for poor mans cocking devices and for a way to send a kid onto the field to kill knights and not be out several silver when the kid died.

Windlass and cranks on the other hand were a way to keep the string centered AND also cock high power bows (some say to 3000lbs by the mid 1600's). My guess is these bows of that power were VERY rare to see or face. They were heavy, took forever to load and took some SERIOUS skills to make and maintain. I would say a common siege bow of 1200 to 1500lbs was common. These cocking devices were for nobles and for bows used for siege. They required heavy bows to blow thru pavices and mortar and in a siege gave time to load these monsters.


Goatsfoots on the other hand are 4:1 levers and offer a way to cock by hand the same weight as a belthook does. They are more expensive and bulky then a belthook however and were reserved really for commissioned bows for the nobles.

On an off note.

If i remember payne galwey's statement he said the heavy he tested was 1200lbs and cocked for hundreds of years. My mentor Robin Allen at http://www.thecrossbowmansden.com/Home.html met payne galweys sister when he was a boy and handled the bows in his book. i'm here to tell you from experiance the prod he explains in his book makes a prod that pulls 1500 to 1900lbs. It is my belief that if the prod remained cocked that long would have lost some tension, but still would have been very usable. Im just not sure of his method of measuring the bows pull weight was accurate or valid.



I know in my testing i consistantly out range heavy (110+lb lonbows war arrow to war quarrel). Not by much, but outranged is outranged. However, a longbows rate of fire i would NEVER keep up with.


I will be traveling to england, scotland and germany at the end of this year for an all access pass to the displays. This includes after hours pass' and the ability to open the cases and handle the weapons. I will also be spending 3 days with war and weapon historians during this visit. I will learn a lot and it is my hope to clear up some of my errors in these weapons i have yet to discover.


Thanks again for the invite and i will keep you posted on the heavy bows coming out and what they can and can not do.
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Gordon Frye




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PostPosted: Thu 18 May, 2006 9:45 pm    Post subject:         Reply with quote

David;

Welcome to the site, and thank you for the informative posts! Crossbows are of interest to me, but it's difficult to find much good, solid information on them, so thank you for coming to the rescue. Do keep us informed as to the results of your research trip to Europe!

Allons!

Gordon

"After God, we owe our victory to our Horses"
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Wolfgang Armbruster





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PostPosted: Fri 19 May, 2006 12:04 am    Post subject:         Reply with quote

This is really great information!
I had no idea that such extremely strong crossbows existed. However I'm glad that I was right in my assumption that crossbows are stronger and outrange longbows *g*

I know people continued to use crossbows for a long time after firearms made their appearance, especially for hunting purposes. But for how long were they used on the battle-field? I was under the impression that people stopped using cross-bows in war in the early 16th century when harkebuses started getting better. Has anybody more detailed information on this? I guess my assumptions are at least partly wrong. Wink
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David Ruff




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PostPosted: Fri 19 May, 2006 8:07 am    Post subject:         Reply with quote

Wolfgang Armbruster wrote:
This is really great information!
I had no idea that such extremely strong crossbows existed. However I'm glad that I was right in my assumption that crossbows are stronger and outrange longbows *g*

I know people continued to use crossbows for a long time after firearms made their appearance, especially for hunting purposes. But for how long were they used on the battle-field? I was under the impression that people stopped using cross-bows in war in the early 16th century when harkebuses started getting better. Has anybody more detailed information on this? I guess my assumptions are at least partly wrong. Wink



This im not really sure of. I know the church put all sorts of restrictions on the crossbow throughout history but i would guess that crossbows were usedwell into the later 1600's as firearms grew. My understanding is that the Germans, Italians and swiss made the crossbow into the firearm. You can see the trigger systems ect that closely follow the later period crossbows of the time. As armor started getting phased out due to weight, the firearms grew more reliable and it was much quicker to load a gun then it was to load a crossbow - hence they fell off the map. Or atleast that is my thinking - will ask that when im over seas.
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George Hill




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PostPosted: Fri 19 May, 2006 8:46 am    Post subject:         Reply with quote

David Ruff wrote:


Windlass and cranks on the other hand were a way to keep the string centered AND also cock high power bows (some say to 3000lbs by the mid 1600's). My guess is these bows of that power were VERY rare to see or face. They were heavy, took forever to load and took some SERIOUS skills to make and maintain. I would say a common siege bow of 1200 to 1500lbs was common. These cocking devices were for nobles and for bows used for siege. They required heavy bows to blow thru pavices and mortar and in a siege gave time to load these monsters.


Pardon me, but this seems.... almost inconceiveable. We aren't talking about something along the lines of a Roman Ballista are we? (IE, on the walls in "Kingdom of Heaven" or some such.)

Can you show us a siege crossbow with something in the picture to measure scale?

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Jean Thibodeau




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PostPosted: Fri 19 May, 2006 9:07 am    Post subject:         Reply with quote

David;

Thanks again for a long and informative post and please keep us informed and consider posting new topics about crossbows and maybe just participate in other topic threads that you find interesting.

I would suggest asking Nathan for status to post new topics on the " Makers and Manufacturers Talk " forum where product announcements and some marketing is allowed and encouraged. You might also consider writing one or more feature articles for this site about crossbows. ( Contact Nathan Robinson by P.M. or E-Mail should you wish to do this. Big Grin Oh, no obligation to do so by the way and I don't want you to feel any pressure. Cool )

Just looking at the shape of the goat's foot lever in pictures I've seen I assumed some variation in the amount of leverage as the lever pushes / pulls ? The amount of pressure applied by the hand might seem constant since the poundage would increase as the lever travels but the leverage advantage would also increase towards the end of the stroke ???

My assumptions may be completely wrong here and you did give a good explanation already about goat's foot crossbows, but I'm still unsure about my above question. Confused Big Grin

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David Ruff




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PostPosted: Fri 19 May, 2006 9:12 am    Post subject:         Reply with quote

Heheeeh.

Something like this exists in show cases; I do not have a picture off hand of a period bow in this weight. I do know there is a company that makes one pulling 3300lbs. Roman ballista’s if I remember correctly pulled 1200 to?? in lbs and launched a 10lb spear out to 250+ yards. It is of my opinion they did the same thing I do in the forge I create my prods in.... Take a piece of steel, heat it, hit it, shape it and what it comes out to - it comes out to. A crank is a 45:1 advantage lever and it is VERY possible to crank up a 3000lb crossbow, it is very possible to have it hold together - these people were not dumb and they did what worked.

What I am saying is, I do not know of any specific examples of period crossbows pulling this weight, however I do know of experts that have guessed to what the weight could have been based on mass and material, and I do know of reproductions pulling to 3300lbs that are supposed to be copies of bows or copies of things that were used and put together free form.


Here is a link of a bow http://www.balestrantica.com/il_diavolo.asp that pulls 3300lbs, or so I have heard. I do not think they may the crank for it however due to legal reasons? Not sure, my translation is not that hot.

Robin Allen is finishing up a 2000lb crossbow based on a true build that existed

Me? That’s too heavy to attempt of even want to attempt.


Last thought; in England today they still pull bolts out of solid stone castle walls. What kind of power does it take to drive a bolt like these (copies of bolts used in and around London LINK REMOVED BY ADMINISTRATORS and drive it into solid stone?

Better yet, battlefield reports of crossbows being able to penetrate 12 inches of bound oak at 100+ paces. I know from my personal bows and from others that I have shot we have not been able to do it on bows upto 1100lbs.
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David Ruff




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PostPosted: Fri 19 May, 2006 9:24 am    Post subject:         Reply with quote

Jean Thibodeau wrote:
David;

Thanks again for a long and informative post and please keep us informed and consider posting new topics about crossbows and maybe just participate in other topic threads that you find interesting.

I would suggest asking Nathan for status to post new topics on the " Makers and Manufacturers Talk " forum where product announcements and some marketing is allowed and encouraged. You might also consider writing one or more feature articles for this site about crossbows. ( Contact Nathan Robinson by P.M. or E-Mail should you wish to do this. Big Grin Oh, no obligation to do so by the way and I don't want you to feel any pressure. Cool )

Just looking at the shape of the goat's foot lever in pictures I've seen I assumed some variation in the amount of leverage as the lever pushes / pulls ? The amount of pressure applied by the hand might seem constant since the poundage would increase as the lever travels but the leverage advantage would also increase towards the end of the stroke ???

My assumptions may be completely wrong here and you did give a good explanation already about goat's foot crossbows, but I'm still unsure about my above question. Confused Big Grin



It seems to me that yes the pressure seems consistent for the most part. That crossbow is really not that hard to cock with that lever. It to me is link hip cocking a 100lb crossbow - easy and quick. But as with all things, I can hip cock 140lbs (placing butt of bow on hip and using hands to span the bow) where most find it very hard to foot cock a 140lbs.

It’s all in how much you do it.


I will see about posting a quick mpeg of the goatsfoot in action and linking it.


Thanks for the information on the other stuff, I might do that. I always have bows and crossbows coming out of the shop. Would be nice to show them off before they goto the floor Happy
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David Ruff




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PostPosted: Fri 19 May, 2006 9:58 am    Post subject:         Reply with quote

Just a quick note:

I have attached a quick video of a goats foot bow cocking from about a month ago. The bow was still untested at this stage so it will not show the bow holding the prod back. The prod itself is rated at 650lbs at 8" of draw. This bow draws 5.5 to 6" with that prod so it should be in the area of 380 to 450 with 450lb being more likely. It topped out a 350lb scale so again - guessing.

It will show atleast how effortless a goatsfoot appears. Actual weight im feeling on the handle is about 90 to 120lbs.

LINK REMOVED BY ADMINISTRATORS

And here is a bow that has not officially gone up on the boards for viewing. It is a target build medieval - not really copying anything from history, just a look cool type bow.

LINK REMOVED BY ADMINISTRATORS

Enjoy
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George Hill




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PostPosted: Fri 19 May, 2006 10:14 am    Post subject:         Reply with quote

David Ruff wrote:
Heheeeh.

Something like this exists in show cases; I do not have a picture off hand of a period bow in this weight. I do know there is a company that makes one pulling 3300lbs. Roman ballista’s if I remember correctly pulled 1200 to?? in lbs and launched a 10lb spear out to 250+ yards. It is of my opinion they did the same thing I do in the forge I create my prods in.... Take a piece of steel, heat it, hit it, shape it and what it comes out to - it comes out to. A crank is a 45:1 advantage lever and it is VERY possible to crank up a 3000lb crossbow, it is very possible to have it hold together - these people were not dumb and they did what worked.


I can believe it could be cocked. Holding togeather.... How thick would the ah.... (shaft? not the prod....) need to be to support 3000 pounds of pressure?

How big would this thing be? Are we talking about a proper mounted siege engine, or a one man portable, shoulder discharged shooting device? IE, Could I stand in an arrowslit shooting one of these things like I would a rifle? (ignoring the issues of reloading)


How large are the heads you mention being imbedded in castle walls? Are we looking at say, spear sized progectiles?

To abandon your shield is the basest of crimes. - --Tacitus on Germania
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David Ruff




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PostPosted: Fri 19 May, 2006 10:52 am    Post subject:         Reply with quote

George Hill wrote:
David Ruff wrote:
Heheeeh.

Something like this exists in show cases; I do not have a picture off hand of a period bow in this weight. I do know there is a company that makes one pulling 3300lbs. Roman ballista’s if I remember correctly pulled 1200 to?? in lbs and launched a 10lb spear out to 250+ yards. It is of my opinion they did the same thing I do in the forge I create my prods in.... Take a piece of steel, heat it, hit it, shape it and what it comes out to - it comes out to. A crank is a 45:1 advantage lever and it is VERY possible to crank up a 3000lb crossbow, it is very possible to have it hold together - these people were not dumb and they did what worked.


I can believe it could be cocked. Holding together.... How thick would the ah.... (shaft? not the prod....) need to be to support 3000 pounds of pressure?

How big would this thing be? Are we talking about a proper mounted siege engine, or a one man portable, shoulder discharged shooting device? IE, Could I stand in an arrowslit shooting one of these things like I would a rifle? (ignoring the issues of reloading)


How large are the heads you mention being imbedded in castle walls? Are we looking at say, spear sized projectiles?



There was a board/stand they used to hold the nose of the bows up, those boards later on were used for powdered guns. these were shoulder shot either like a modern rifle with the butt of the stock agaist the should OR over the shoulder. I would guess that a 3000lb crossbow would be in the area of around 30 to 50lbs.

The bolts i have that are copies of bolts found in the tower of london are 10" long (not including the tip) and are fletched with leather vanes. The shaft is 5/8"" thick 2.5" behind the shaft front and tapers to 3/8" at the tail. The vanes are about 3.5" long and stick out 1/2". The tips were of many types depending on the area, the blacksmith and what you were shooting. A typical bodkin was about 3" long, 1/2" wide at the head and weighed in at about 400 to 500 grains. Total bolt weight was around 700 to 1200 grains sometimes more - again depending on area, maker and what you were shooting.

this type of bolt as explained above would be fine for a ultra heavy crossbow, bolt speed off the bow would be in the 180 to 200 feet per second area, inch pounds of force off the barrel of the crossbow on a 3000lb would be in the 16,500 in/lbs area as compared to say a modern excalibre crossbow that produces 3375in/lbs or a barnett type in the area of 1500 to 2100inlbs OR finally a average 120lb english longbow in the range of 2400 to 2700 in/lbs.


As a comparison my 380/450 goatsfoot bow produces 2280 to 2700 in/lbs and is verified in putting a bolt completely through 12 gauge sheet steel, then hitting and going through 18gauge back steel plate and having enough energy to stick 1.75" into a hickory tree.


To answer what kind of bolts have been found and recovered from castle walls - the kind that i have are typical of them. Granted the wood is long gone, but the heads were buried inches into the stone and mortar.

Finally, yes one could be used in an arrow slit. However mainly ( i believe) these bows were used to raze pavices and seige engines. I say this as 250yards is about the outside range of a seige engine and of a heavy crossbow. It is pushing it for a stout longbow. Even at that a long bow is not going to cause death at that range where a crossbow with a heavier missile will as it retains its energy and speed better then an arrow.

I have read accounts that crossbows were used as sniper rifles. A shooter would hide along the castle walls in the early mornings waiting for a guard to do his business over the wall - click - dead guard. Also i have read accounts of crossbows being used against arrow slits due to the accuracy and power. A bolt gets thru and it kills, if it doesn't in proceeds to bounce of walls, thru doors and into people. Catch a corner of the slit - the slit shatters and sprays mortar and stone back at the people inside, the bolt shatters and sprays, the head buries into stone, people and such.


A crossbow, no matter a 450lb or a heavy war bow were set at a "point blank" range, this range was usually 60 to 90 yards. This ment if i aimed at a mans head, i would strike no lower then his throat. These weapons were VERY accurate out to 150 yards - accounting for drift ect. Hitting a arrow slit, a knight or a leather armored man was/is not hard to do, infact its about as easy as a few days practice.


Hope that helps Happy
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Benjamin H. Abbott




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PostPosted: Fri 19 May, 2006 8:29 pm    Post subject:         Reply with quote

Quote:
Total bolt weight was around 700 to 1200 grains sometimes more - again depending on area, maker and what you were shooting.

this type of bolt as explained above would be fine for a ultra heavy crossbow, bolt speed off the bow would be in the 180 to 200 feet per second area, inch pounds of force off the barrel of the crossbow on a 3000lb would be in the 16,500 in/lbs area as compared to say a modern excalibre crossbow that produces 3375in/lbs or a barnett type in the area of 1500 to 2100inlbs OR finally a average 120lb english longbow in the range of 2400 to 2700 in/lbs.


Huh? A 1200 grain bolt going 200 FPS would only have about 145 J. The average longbow probably had a 150lb draw and could manage 146 J with a heavy arrow.
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David Ruff




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PostPosted: Sat 20 May, 2006 8:20 pm    Post subject:         Reply with quote

Benjamin H. Abbott wrote:
Quote:
Total bolt weight was around 700 to 1200 grains sometimes more - again depending on area, maker and what you were shooting.

this type of bolt as explained above would be fine for a ultra heavy crossbow, bolt speed off the bow would be in the 180 to 200 feet per second area, inch pounds of force off the barrel of the crossbow on a 3000lb would be in the 16,500 in/lbs area as compared to say a modern excalibre crossbow that produces 3375in/lbs or a barnett type in the area of 1500 to 2100inlbs OR finally a average 120lb english longbow in the range of 2400 to 2700 in/lbs.


Huh? A 1200 grain bolt going 200 FPS would only have about 145 J. The average longbow probably had a 150lb draw and could manage 146 J with a heavy arrow.



Bolts retain energy better down range where an arrow sheads it much faster. Also remember a crossbow can fire a much heavier missle then a bow could. Something within the physics of the bolt seems to impart a lot more shock at range then an arrow does.

Shooting my 117lb longbow and the 450lb crossbow - the crossbow blows thru thicker material at 50+ yards where the longbow starts to peter out at 60+ yards as far as doing the damage it would take for a fatal hit.
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Florian H.




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PostPosted: Sun 21 May, 2006 7:38 am    Post subject: A physical point of view         Reply with quote

Quote:
Bolts retain energy better down range where an arrow sheads it much faster. Also remember a crossbow can fire a much heavier missle then a bow could. Something within the physics of the bolt seems to impart a lot more shock at range then an arrow does.

Shooting my 117lb longbow and the 450lb crossbow - the crossbow blows thru thicker material at 50+ yards where the longbow starts to peter out at 60+ yards as far as doing the damage it would take for a fatal hit.


This might be because an arrow shot from a bow is much longer => a)has more surface exposed to the airstream, and b) also the fletches are bigger and project further beyond the boundary layer into the airstream. This causes a) more friction drag and b) more interference drag. This results in an aerodynamical advantage for the crossbow bolt. If the crossbow bolt is heavier than the longbow arrow, also the relation between impetus(momentum) and kinetic energy of a crossbow bolt is much higher. The differentation of the momentum along time is the force acting on a system. In the case of a crossbow bolt to change momentum means to change velocity, since its mass is constant (except for destruction). That means that to decelerate a crossbow bolt a much bigger force is needed as for the longbow arrow. But as mentioned befor, a smaller aerodynamical force is acting => a crossbow bolt, which could to a certain degree even be lighter then an arrow keeps his velocity more constant => his kinetic energy also, than an arrow fired from a longbow.

On impact the kinetic energy is gradually transformed into destructive energy to penetrate the target. But this transformation is affected by a degree of efficiency. A longbow arrow is longer has a smaller diameter. That means it is not so stiff as a crossbow bolt is. As the arrow impacts, a share of the kinetic energy is consumed by the compression and vibration of the arrow. This energy is lost for the process of penetrating the target. A crossbow bolt will wobble and compress also of course, but according to its shorter lenghts and higher stiffness these side effects are much less pronounced. So the degree of efficiency for the impact of a crossbow bolt is much higher than for an arrow, so it can use more of its kinetic energy to impact its target.

So concludingly can be said, that a heavy crossbow bolt travelling at high velocity can keep its velocity longer, that means it has a higher kinetic energy on impact and its impact even has a higher degree of efficiency. So a fast travelling, heavy crossbow bolt is certainly more devastating than a comparable arrow fired from a longbow
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Jean Thibodeau




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PostPosted: Sun 21 May, 2006 10:28 am    Post subject:         Reply with quote

As to ideal weight of a crossbow bolt to get the most power on impact one can increase the weight of the bolt to a great degree with a very heavy powerful crossbow: A small lost of velocity is negligible compared to the energy of a much greater mass moving just a little slower.

But how much is too much ? What would be the weight ideal for a bolt to get maximum velocity ( No point going so light that a lighter bolt has almost the same velocity. ) versus the maximum weight of bolt where any increase in weight would total less energy or momentum, momentum which might be more relevant to terminal effect than kinetic energy when dealing with the relatively low velocities of arrows and bolts compared to bullets were kinetic energy of a 3000 ft/sec projectile becomes relevant.

( Well, the whole subject of kinetic energy versus momentum is responsible for the death of many trees to make the paper of gun magazines over the years and maybe we should not go there ? )

What would the ratio between these bolt be ? If one gives the light bolt a value of 1 would the heaviest bolt be 1 1/2, 2 or more in weight ? Maybe figures in ounces would help visualize the weight of bolts easier on us who don't relate to weight in grains in a meaningful way: Number of bolts to the pound maybe ? Sort of like shotgun gauges maybe: 12 bolts to the pound or 24 bolts to the pound would be an easy scale to understand.

Would a siege crossbow in the 2000 pound range have a figure ( gauge ) of 4 to the pound ? Is a 1 pound bolt totally realistic or ridiculously heavy ? Now, with a large siege engine like the Romans used the bolts might get into the spear range in size and weight ?

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David Ruff




Location: Denton TX
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PostPosted: Sun 21 May, 2006 8:51 pm    Post subject:         Reply with quote

Jean Thibodeau wrote:
As to ideal weight of a crossbow bolt to get the most power on impact one can increase the weight of the bolt to a great degree with a very heavy powerful crossbow: A small lost of velocity is negligible compared to the energy of a much greater mass moving just a little slower.

But how much is too much ? What would be the weight ideal for a bolt to get maximum velocity ( No point going so light that a lighter bolt has almost the same velocity. ) versus the maximum weight of bolt where any increase in weight would total less energy or momentum, momentum which might be more relevant to terminal effect than kinetic energy when dealing with the relatively low velocities of arrows and bolts compared to bullets were kinetic energy of a 3000 ft/sec projectile becomes relevant.

( Well, the whole subject of kinetic energy versus momentum is responsible for the death of many trees to make the paper of gun magazines over the years and maybe we should not go there ? )

What would the ratio between these bolt be ? If one gives the light bolt a value of 1 would the heaviest bolt be 1 1/2, 2 or more in weight ? Maybe figures in ounces would help visualize the weight of bolts easier on us who don't relate to weight in grains in a meaningful way: Number of bolts to the pound maybe ? Sort of like shotgun gauges maybe: 12 bolts to the pound or 24 bolts to the pound would be an easy scale to understand.

Would a siege crossbow in the 2000 pound range have a figure ( gauge ) of 4 to the pound ? Is a 1 pound bolt totally realistic or ridiculously heavy ? Now, with a large siege engine like the Romans used the bolts might get into the spear range in size and weight ?



In this case here is how i tune my bolts. for any bow i build.......


I start with a bolt - the weight is decided on the power of the bow. But it is a low weight.

I fire the bolt and check its speed - record it.

I then fire progressively heavier bolts until i get a marked decrease in speed. Say the first bolt fires at 210fps and i go thru 6 bolts and i am at 190 fps. thats where i will stop.

History seems to say the longbow and crossbows fired around the same speed - 170 to 190 fps. Some bows fired even slower. So i figure that a shot at 190 to 200fps is about right.

A crossbow prod made of steel will only zip that bolt out at one speed. This is due to the limbs and its ability to move. A heavy bolt of a heavy bolw "should" move at the or very near the speed a light bolt. Once you see a dramatic decrease in speed - thats where your firing to heavy a missile.


FYI, on the big 1700lb crossbow i am making - it will fire 3/8" steel rods fletched with leather and a bodkin tip ground into the front. Steel bolts were used back then - this becomes a pure armor piercing round much like a 50 cal.


David
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