Kinetic Energy (Joules)

Discussion in 'General Slingshot Discussions' started by DaveSteve, May 14, 2012.

  1. DaveSteve

    DaveSteve New Member

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    I checked for info about the appropriate ammo for hunting. I found that the most recommended ammo for hunting is 12mm steel or 12 mm lead. It is also mentioned to use 'strong' bands. I read about Dankung 2050, Trumark black, double TB gold, etc. <br><br>People talk about to kill rabbits at 50m. ? <br><br>What I'm interested it : What energy (joules) would be neccesary to achieve this?<br><br>Right now my trajectory at 50m would look like a rainbow.<img src="http://illiweb.com/fa/i/smiles/icon_biggrin.png" alt="Very Happy" longdesc="1"> Just kidding.
     
  2. Ryan Wigglesworth

    Ryan Wigglesworth Senior Member

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    <div>50 meters... holy shit.<br><br><br>I have yet to aim at anything living, i have only shot myself <img src="http://illiweb.com/fa/i/smiles/icon_razz.gif" alt="Razz" longdesc="9"> so i can't say, but really you have to have amazing accuracy to pull that shot off !!! Sure I can hit a can at 10 meters, or 20 meters even. but what power is being delivered to the target ? cant be much... then again i heard rabbits are easy kills..<br><br><br>also, out walking i get pretty close to urban rabbits, about 20 meters or less till they stop and raise their heads to see whats moving... so 50 meters is pretty far for a rabbit... ? <br><br><br>165 feet .... well its possible i guess... <br><br><br>sorry i cant help much! this is a neat topic tho <img src="http://illiweb.com/fa/i/smiles/icon_biggrin.png" alt="Very Happy" longdesc="1">
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  3. JoergS

    JoergS Administrator

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    50 meters is a long distance for a slingshot. But it is doable. If you can hit a can at 10 meters, you can hit a shoebox at 50 meters. <br><br>Energy wise, the speed loss is not so significant. And rabbits are indeed easy to kill, very soft and vulnerable animals. <br><br>The advantage of hunting rabbits from that kind of a distance is that the animal often does not run when you miss. The sound of the shot will be far distant and not alarm the rabbit. A miss in soft ground is also no reason to jump away. The rabbit may hop on a meter or so, that is all. So you can have several attempts.
     
  4. DaveSteve

    DaveSteve New Member

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    I would never try to shoot a rabbit at 50m. <br><br>I'm just curious what it would take to do so. <br><br>How do you define a powerful slingshot?<br><br>Probably not so easy to come up with a number in Joule, isn't it?
     
  5. mr_paradox

    mr_paradox New Member

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    The speed loss is significant.<br>My neighbor alleged that my 22 air rifle was punching holes in his fence.<br>His fence is 60 meters away from my where I was shooting.<br>At 10 meters I can kill a rat with my 22, and it will punch thru 1/2 inch plywood easily. At 40+ meters it will just dent the plywood, sticking into it.<br>The drop for my air rifle zeroed at 20 meters, at 40 meters is almost 3+ inches (if i remember correctly)<br><br>I then did a search on google, my rifle seems to have similar charactarisitics to this one.<br><a href="http://www.velocitypress.com/air_rifle_ballistics.shtml" target="_blank" rel="nofollow">http://www.velocitypress.com/air_rifle_ballistics.shtml</a><br><br>At muzzle velocity 850 feet per second.<br>60 meters velocity has dropped to 400 feet per second<br><br>Energy = 1/2 m v^2 <br>Initially 23 ft pound<br>60 meters it is around 5 ft pound<br><br>To illustrate.<br>I have heard of guys being hit by a 9mm pistol round at 300 meters and it not even penetrating them.<br><br>A 15mm lead ball is ~20 grams<br>A BB/pellet is about 0.57 grams<br>So it probably possible to kill a rabbit at 50 meters.<br><br>Spheres are very bad for drag compared to "bullets".<br>But i found on google a "ball speed calculator" so you can get an idea of velocity at certain times.<br><a href="http://www.jayandwanda.com/tt/ballspeed_calc1.html" target="_blank" rel="nofollow">http://www.jayandwanda.com/tt/ballspeed_calc1.html</a><br><br>I don't know how accurate the ball calculator is.<br>When I punched in the numbers for a 15mm lead ball at initial velocity of 100 m/s it showed at 1 second of travel time it would be still 80+ meter per second.<br><br>It also said that dimples/imperfections on the ball can increase drag a lot.<br>Hmmm.<br><br>I don't know.<br>If someone could find / do better experiments in this area <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2">
     
  6. JoergS

    JoergS Administrator

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    The heavy, slow slingshot balls are much less decellerated by the air resitance. At 50 meters, the speed will still be quite high. <br><br>I have never seen anyone who can shoot a 15 mm lead ball (20 gramms) at 100 m/s - that would be 100 Joules of energy. 75 m/s is a much more realictic value. <br><br>But even then I estimate the ball will still have 50 m/s at 50 meters, at least. That is a solid 25 Joules.
     
  7. mr_paradox

    mr_paradox New Member

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    So a 25mm ball will be 4 times the size.<br>So that is 100 Joules <img src="http://illiweb.com/fa/i/smiles/icon_wink.gif" alt="Wink" longdesc="15"><br><br>I just used 100 m/s to illustrate.<br>I am a "slingshot" newbie.<br>To be honest I am not really into slingshots, but more into xbows.<br><br>I am pretty much bored with guns.<br>I am used to rifles <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"> A 7.62mm has a muzzle velocity of 850 m/s<br>A 5.56mm is 940 m/s<br>So I am not used to low velocities <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"><br><br>Basically 6 months ago, I was on a job site supervising.<br>Usually I play with my air rifle but it got boring.<br>So I made a tiny catapult out of bamboo for my kid.<br>I then somehow found this site, and got into making xbows.<br>I have just made 3.<br><br>Also I am learning a lot about wood working techniques, which is also helpful for my job <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"><br><br>Hopefully when rainy season comes, things will slow down, and I will have time to experiment. I would like to make a ballistic pendulum.<br><br>Gun laws in the Philippines are "weird".<br>You are not allowed to buy anything with 7.62 rounds.<br>7.76 is too "dangerous".<br>But 5.56 is fine.<br>Also you are allowed to buy assault shotguns, a submachine gun.<br>I don't own a submachinegun, despite the gunshop trying to sell me one all the time <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"><br><br>Anyway I get a lot of pleasure from making something that shoots, and the theory interests me a lot. So I got Jorge to thank for that <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2">
     
  8. brat boon

    brat boon New Member

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    <div>maybe bill hays can do that?</div><div class="clear"></div><div class="signature_div">
    <br><strong>at school, I am a slingshot expert</strong> <img src="http://illiweb.com/fa/i/smiles/icon_biggrin.png" alt="Very Happy" longdesc="1"><br><br>on this forum a noob <img src="http://illiweb.com/fa/i/smiles/icon_neutral.gif" alt="Neutral" longdesc="20">
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  9. JoergS

    JoergS Administrator

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>mr_paradox wrote:</b></span></td></tr>
    <tr><td class="quote">So a 25mm ball will be 4 times the size.<br>So that is 100 Joules </td></tr>
    </table>
    <span class="postbody"><br><br>Not really. The formula for energy is 0,5*mass*velocity*velocity.<br><br>A 25mm steel ball weighs 65 gramms. If you can shoot that one with 75 m/s, it has 182 Joules initially, and if it drops off to 50 m/s, then 81 Joules are left. <br><br>But noone can shoot a 25 mm steel ball at 75 m/s from a conventional slingshot. I have done 55 m/s, and maybe I can get to 60 m/s. <br><br>My winch operated slingshot crossbow would be the best chance.<br><br>But don't forget that the "stopping power" is largely determined by the momentum, not by the energy of the projectile. Slingshot ammo outperforms many firearms rounds in terms of momentum.<br><br><a href="http://slingshotchannel.blogspot.de/2011/02/slingshots-stronger-than-firearms.html" class="postlink" target="_blank" rel="nofollow">Read my related blog entry!</a></span>