Crossbow changes?

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Crossbow changes?

Postby Syrus » Fri Jul 21, 2006 3:22 pm

In accordance with the math in http://www.geddon.org/index.php/Crossbow_Rules_Development, does anyone else want to safety-test 35# crossbows for a feasible change in our current ruleset?
Last edited by Syrus on Fri Jul 21, 2006 3:54 pm, edited 1 time in total.
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Postby savetuba » Fri Jul 21, 2006 3:38 pm

I have a 50lbs Cbow that has been used several times. The problem arises when the saftey of the Cbow its self is in question. I remember finding a site that sold Cbow parts so you can make your own custom Cbow, but if the draw is a long draw that means you must pull the string into place, ussually meaning a metal foot loop on the front of the weapon. IE A saftey hazzard.

the 50# Cbow I use has a pistol grip and when it lands on the ground it is a large saftey hazzard (tripping).

a chinees repeater might be ok, but I havn't tried it yet.
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Postby Kage » Sat Jul 22, 2006 1:24 am

The tripping factor of cross bows is no different then tripping over a shield or another fighter that is laying on the ground. One fighter in Ebohold was able to create a safef workable cross bow that he built bu hand. I asked him to bring it to chaos wars x and he said that he would so people could have a look at it and what not.
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Postby Syrus » Sat Jul 22, 2006 1:11 pm

What was the poundage on his crossbow?
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Postby Forkbeard » Sun Aug 20, 2006 8:08 am

I'm behind changing the rules for Xbows all the way. I've been shot by a few "high" poundage xbows with padded arrows and they have all been perfectly safe.
Our Xbow rules weren't based on anything more than the idea of the half draw, nothing practical.
I'm sure if some one did some real good testing of how much force is applied by the arrow from different kind of bows and Xbows and recorded the info scientificly we could get people to think about changing this rule.
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Postby Kage » Sun Aug 20, 2006 5:30 pm

I dont know what the poundage is but I do know the feet per second of it came out around 220 fps. While a normal 35# bow came out around 450 fps. When I can get an actual poundage I will post back but I know that his string is just a normal braided bungee cord you can pick up at Walmart.
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Postby Olos » Thu Aug 24, 2006 2:22 pm

Kage wrote:I dont know what the poundage is but I do know the feet per second of it came out around 220 fps. While a normal 35# bow came out around 450 fps. When I can get an actual poundage I will post back but I know that his string is just a normal braided bungee cord you can pick up at Walmart.



try again on those numbers...

my 62 pound(around there) hoyt compound with 425 grain aerodynamic arrows gets about 240 or so feet per second, around 270 if i bring it up to 70 pounds. my 48 pound recurve gets around 190

I'd guess a foam fighting bow to be around 50-100 feet per second on arrow speed....
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Postby Oznog » Tue Nov 28, 2006 2:20 pm

Greetings. Oznog of Amtgard here, I've been an LARP archery engineer for over 15 years and have done a lot of work with crossbows. Jikanta has been so kind as to make an exception to the forum permissions to allow me to provide a consulting opinion on this subject.

I believe the calculations listed on the BelegarthWiki http://www.geddon.org/index.php/Crossbow_Rules_Development are incorrect due to a misunderstanding of the definition of draw length. I have put my comments on this in the Discussion area of the wiki article.

The math discussion aside, the important point is that a rule must multiply power stroke (string's travel distance) by poundage to be useful. Power stroke is just as important as the poundage is in determining the strength of the crossbow. Double the stroke distance, double the power. If you don't specify the stroke distance, you don't know what the power is.

We do not allow headshots in Amtgard, but we do use the exact same poundage handbows. 450 inch-pounds is about 2/3rds draw (or a 24 lb bow at full draw), has been shown to be safe and complaint-free at close range with well constructed arrows. Getting much below 400ip starts to slow them down enough that many fail to even notice them. 350ip borders on impractical for this reason. As I mention in the Discussion article, it is important to note that crossbow bolts have less shaft weight which lessens the job of what the impact padding needs to do.

Crossbow design is often done with fairly crude fiberglass or wooden prods. These can be less efficient and shoot at lower energies than the inch-pounds predict. I can say that the 450 ip we decided on was determined using what is probably the most efficient crossbow prod possible.

In some ways I can say that crossbows actually have a safety benefit. Handbows have the capacity for archers to reduce the draw at close range while crossbows cannot. This sounds like a benefit at first, but then you realize that you're relying on the shooter to actually do this and many don't do it with 100% reliability. Limiting crossbows to a lower power IS 100% reliable and this hard limit is generally desirable.

Incidentally, as far as speed is concerned- a projectile's energy is the mass times velocity squared. Shooting an arrow out of the same mass from a bow of half the poundage will launch at 70.7% of the initial speed, not 50%. The impact energy will be half as hard like you'd expect.

I use 2.5" diameter arrows that are very light on a very good 35# bow and have shot up into the 115+ fps range as measured on a chrono. Crossbow bolts are more in the range of 97 fps or so, but they are somewhat lighter due to the shorter shaft. With a heavy design, you might be down to 90 fps on a good bow, could be down to under 80 fps on a poor 35# bow.
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