Primitive Archer
Main Discussion Area => Bows => Topic started by: Tracker0721 on March 31, 2016, 02:44:25 pm
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So I got a chronograph to test my air rifle and build up some hunting data for different pellets and I decided to shoot my 55@27 Selfbow through it. With my 485+- Doug fir arrows I'm getting 162fps for an average. With my 770 grain ocean spray arrows(what I plan to hunt with) I'm getting 124fps. 88fps is 60mph so I figure my arrow with a sharp obsidian tip will kill something deader then dead for sure. Anyone else have some numbers to compare? This isn't a speed thing really, more of an efficiency thing.
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Keep them light. Personally I dont care as long as I come close to the bulls eye and I enjoy Archery and the camaraderie for what its worth. :)
Today I was shooting arrows with 125gr tips and new ones with 145gr tips seems like the 125gr were better Flying. All shafts are 40# spine. And I shoot them from 35# bow and a 43# bow. I give up on trying to rationalize everything. I found out years ago that been a perfectionaist drove me nuts and discovering that I had obsessive compulsive disorder behaviour to a certain degree. >:D
Enjoy the shoot forget the technicalities ;D
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well i have alot of numbers going back 20 years or so,,,I think 30, wow it goes by fast(no pun intended)
your bow seems to have nice cast,, 162 fps with the 485 grain arrow is a good hunting combo,, fast enough to get to a deer before it jumps too far,, but heavy enough to do the job,, the slower arrow will work for sure,,,,
I just finished an osage bow,raw hide backed,,55 ntn ,50@25 inches 157fps with a 500 grain sitka spruce arrow,, 12 strand fast flight with fur silencers,, it is nice cast for me with a hunting set up,, I plan to shoot 500 to 700 grain arrows to hunt deer,, I like the fast 500 grain arrow,, that being said I shot a deer last year with a 700 grain birch slow arrow,,,, so I guess what shoots best for you out of your bow is the way to go,, :)
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You can compare the energy using 1/2 m times v squared... don't worry about units as long as you are consistent.
So the 485gn at 162 fps gives 6364170 units of energy
The 770gn at 124fps gives 5919760 units of energy which is less, so I'd say you are going a bit too heavy at 770 gn as you are loosing speed and energy.
Del
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I think your test was flawed, I would recheck. The 770 arrrow should have more energy instead of less. Maybe you didn't draw them the same. Bows are always more efficient with heavy arrows. The 770 arrow should have been closer to about 135 fps or so. I think you should select an arrow weight that gives you at least about 150 fps for easier aiming.
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You can compare the energy using 1/2 m times v squared... don't worry about units as long as you are consistent.
So the 485gn at 162 fps gives 6364170 units of energy
The 770gn at 124fps gives 5919760 units of energy which is less, so I'd say you are going a bit too heavy at 770 gn as you are loosing speed and energy.
Del
Thanks for making it blatantly obvious which is the better choice! You see, I was about to chime in and say to go with the heavier arrow since sheer weight leads to improved penetration, but that would have been wrong. You made me stop and think about the thru-and thru I got with a mere puny 425 grain arrow in a large heavy bodied mule deer years ago.
With the drop in arrow speed, you are looking at a lot more drop in point of contact, so the faster arrow means less futzing around with calculating or compensating for drop.
Good luck with your setup!
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Del that looks right on paper for sure, but the 700 grain arrow will give great results on game, and usually better penetration,, there is something in the calculation that does not account for the amount of energy that goes into the arrow,, the way I understand it ,, is that the heavier arrow is able to take more energy from the bow than the lighter arrow,, I am not good at math ,, so someone might be able to explain it better or in a more clear way,,,,but I do have alot of experience shooting hogs with different weight arrows,, and even though heavy might be slower,, they have had better penetration in my experience,, I do like the lighter arrow for deer,, as they do move at the sound of the arrow,, and I feel the lighter arrow gives me just a bit of an advantage,, this debate had gone on forever,, and I just have my personal experience to go on,, :) the deer I shot last year was with a 700 grain arrow through the top of the shoulder and came out the other side toward the bottom of the deer,, I was shooting a bow in the range of the 55# bow mentioned from above,, if a lighter arrow would have done better,, it would not have been noticeable at the range I was shooting,,
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Brad, I believe you are correct. Del is also correct but it appears to me that the arrow speed test was off. I have tested arrows from 100 grains all the way up to 4,000 grains. Heavier arrows always take more energy from the bow. Not as good fro trajectory but for penetration they will do better. I believe that he need to retest both arrows, one of them was a bad test.
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Brad I get your point. Sometimes lighter arrows don't seem to work as well. But Del is right. The velocity of the arrow directly relates to its energy. The transfer from the bow is more about limb efficiency and spline but in the end it's 1/2 mv squared. To your point, a stiffer arrow transfers that kinetic energy more to the prey of choice, via the pointy end, versus more vibration and flex.
Side note: I've met many a hunter, that partakes in variety of hunting methods, who gets drawn into the "heavier is always better" group from a misplaced idea about the takedown power of their projectile. No offense intended to anyone but the velocity required to achieve this physical phenomenon is unattainable by a bow, crossbow, and many a firearm.
Congrats on 162 fps. That will get the job done. Happy hunting.
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thank you Steve for explaining that so clearly,, :)
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Yes, I was only going by the figures given.
Here is a post where I increased the weight of a crossbow bolt and plotted the energy.
The heavier the bolt the higher the energy up to the point where you can only get out the energy you put in.
http://bowyersdiary.blogspot.co.uk/2011/11/mass-velocity-and-energy.html (http://bowyersdiary.blogspot.co.uk/2011/11/mass-velocity-and-energy.html)
There is a point on the graph where increasing weight doesn't make much increase in energy, but does start loosing speed. It shows there is an optimum trade off point.
No point having a quarter pound arrow for maximum energy if it is so slow it can't reach the deer! ::)
I've attached the graph, Red line is energy. Blue line is speed.
You can see that at about 20 grams (308 grains) the the energy is pretty much up to full and heavier than that the speed drops off without much gain in energy. Note this is only a low power crossbow pistol 50# at short draw (about 6") so the optimum weight for this isn't the same as the optimum weight for the bow we were discussing.
On this graph, compare the arrow speed at the 2 weight we've been discussing (approx 30 grams and 50 grams) you'll see the energy is similar but the velocity is way down on the heavier arrow.
I'd guess that the speed figures in the original post are just a bit out (as Badger suggested) and that the two energies are probably similar. There is plenty of experimental error in my graph and that is with a crossbow, it shows how hard it is to get good accurate results!
Del
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I'll have to test again. My ocean sprays fletchings were a little too tall and I only shot 3 times. I think that and I was shooting from about 2-3 yards. I wonder if the obsidian tip on the OS played a part too since I had a steel point on the Doug fir shaft. So I guess I'll go back and cut the fletchings the same, paint my obsidian tip black and shooting all from a measured 6 feet. Didn't know we could go all high speed, mathematical, awesome on this. I'll get my chronograph and notepad! Haha
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Thanks for the explanation Derek. A picture says more than a thousand words (if you can read what's on the axes >:D)
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I'll have to test again. My ocean sprays fletchings were a little too tall and I only shot 3 times. I think that and I was shooting from about 2-3 yards. I wonder if the obsidian tip on the OS played a part too since I had a steel point on the Doug fir shaft. So I guess I'll go back and cut the fletchings the same, paint my obsidian tip black and shooting all from a measured 6 feet. Didn't know we could go all high speed, mathematical, awesome on this. I'll get my chronograph and notepad! Haha
At 2 or 3 yards, the fletching and point shape won't have time to make much difference as their effect will be aerodynamic and it's not in the air very long... on a flight shot they will make a big difference.
Del
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I think that 162fps is very respectable given the bow specs.
I find that my very best selfbows shoot just about (100 + draw weight) FPS at my 25" draw with an arrow of just under 500gr. So my best 50# selfbow I might expect to get just about 150fps with 480-500gr.
Lighter bows seem to do slightly better, for example my 36# selfbow shot 138fps, 51# bow shot 150fps, so this is just a rough guideline.
This probably happens because of the fact that the (100+draw weight) is a linear approximation of what would probably be a logarithmic curve.
Tri-laminate wood bows seem to do better. They tend to run just under about (100 + draw weight (1.1-1.2)) or so.
So a 50# tr-lam I would expect to shoot just about 155-160 FPS in a best case.
My 62# tri-lam recurve shot 174fps, for example .... Slightly better than expected
My 46# tri-lam longbow shot 150fps ... Slightly lower than expected according to the formula.
These are just my results, with my draw and release. My main use of the chronograph is to
1: compare my bows to each other on the same day with the same arrows.
2: practice a perfectly consistent anchor point and release. If you can shoot repeatedly within 1 or 2 FPS, you are consistent.
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What I was thinking Del was the obsidian wasn't casting a shadow the same through each sensor so it'd be just like when shooting shiny pellets and causing the sensors to figure the wrong speed. That's why people color their pellets black at the nose when they're getting big differences in FPS. I was just spit balling with the feathers height. Didn't get to shoot today but will tomorrow.
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Seems so me like you're spending a lot of time worrying about arrow weight when you could be practicing your accuracy......and if you could hit where you need to, the arrow weight won't make any difference.
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Just a comparison here that is related.Years ago a big game hunter Elmer Keith solved the penetration problem for African big game by going with a heavier bullet for better penetration.Instead of a lighter bullet with more powder.Same principal with arrow shafts also.
Shoot an arrow in water once.It goes deeper with more punch than a lighter lead bullet.All because of the mass the arrow carries.
With archery what's most important overall is placement and flight amongst other things of course.When you get it all together it can count in a situation that needs it.
Flat shooting 11 grain per pound arrow at 20 yards is what I go for and use hunting.That's all I want to practice with too so I can become as accurate as possible since I'm not the best shot all the time.....lol..So my 52#@28" bows that I like to shoot will shoot a 560 to 580 grain arrow consistently somewhere around 155 to 160 fps.Some bows have shot better into the 170's.Those I'll shoot a heavier arrow yet into the 600's or more.Goal here is to enjoy the lighter draw weight with the punch of a heavier bow.
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Yes Drewster, I could be practicing accuracy but wouldn't you wanna know the optimum arrow weight for your bow? Then figure the optimum point weight to shaft weight? Haha I take it not but still! I mean, I practice my accuracy everyday. I was just curious at the start what other people where getting and if it could be used to make something primitive more modern. But now that Del brought up the point about an optimum spot, my curiosity wants to find it.
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Your optimum spot is easy to find. The heaviest arrow will always be the slowest yet carry the most energy. You need to find an acceptable arrow weight for the game you are killing that is fast enough to be accurate with. Your 475 arrow is plenty heavy enough for deer and gives you good speed, I don't think I would want to go below 150 fps so if I were in your shoes I would choose something about 500 to 550 grains.
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I think some are getting energy and momentum mixed up a bit. Energy out of a "system" should not change much but is dominated by velocity. Hence why velocity is squared.
But for primitive archery or even for compounders, momentum is king for penetration. MassXvelocity. That's the reason, most 45-70's will outpenetrate a 30-06, even if they have the same energy or even if 400gr projectile has less energy than the 150gr out of the 06.
But momentum on the other hand is key for penetration. Your 770gr arrow will carry more momentum.
This is the age old argument folks have talked about around campfires, where you have one group, usually younger gen, who think super fast whiz bangs are best, and old timers like Col. Cooper always thought heavier is better. I myself like to keep my arrows around 150-160fps, that way my mind does not have to totally retrain to shoot different bows.
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Tracer0721....The principals versus primitive to modern are the same.Don't know quite what you mean by that question making something primitive more modern.Your subject is tip toeing around making primitive bows efficient I'm gathering is what you mean.What Badger is saying is correct just from my limited experience compared to his since he has tested countless more bows than me.There can be quotes of deer shot dead with 350 grain arrows but I'm sure the placement was right.At close range it's practically irrelavent anyway [under 20 yards].The longer the distance shot the lighter arrow will lose more energy while the heavier arrow will maintain more when hitting the target.I don't have a graph to prove this just experience shooting things that's all.If I could be a crack shot at 50 yards that would be nice but I'm not.Not even close to that.....lol.When hunting I want as many things in my favor as possible no matter what.It's good you are shooting first off to find out that's what's most important too.You'll find out soon enough what pleases you.
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I think some are getting energy and momentum mixed up a bit. Energy out of a "system" should not change much but is dominated by velocity. Hence why velocity is squared.
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What you say makes sense, but isn't actually quite right.
Look at the graphs I plotted...
Yes energy out doesn't change much, once you have a heavy enough arrow
You'd think the velocity squared would dominate... but below that optimum weight. it doesn't!
Again see the graph... with the lightest bolt I got over 200fps, but the energy (and momentum) was far less than the heaviest arrow.
That's the whole point of doing all those tests and plotting the graph.... to see where common sense and intuition breaks down and and the actual performance of the system takes over.
The optimum is the arrow that is getting close to that maximum energy, whilst having the highest velocity, and thus most momentum, which is what I think you were alluding to.
Taking it to the limit, the arrow with zero mass is fastest, but it has no energy or momentum >:D
Del
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I am still going to say the lighter arrow is THE best choice. And here is my reasoning:
1) it has more than enough weight to penetrate a deer. Deer are not armor plated, no matter what the .300 Win Mag shooters may think. A sharp projectile moving at the speed of this arrow is more than sufficient to pass thru both sets of ribs and set the lungs to bleeding profusely.
2) a heavier arrow will suffer more drop on trajectory based on distance from the shooter to the target, requiring split second calculations and opening Pandora's box by adding another level of complexity. It's the plate spinner in the circus...he keeps adding plates and having to dash back and forth to keep it all up in the air at once. Great fun only happens when it all crashes to the ground.
Fastest arrow with enough momentum and energy to penetrate is the simplest solution.
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I agree that the 150fps is a good starting point for hunting arrow speed,, I have hunted with bows that shot faster and slower,, it is good to know what your hunting set up is doing,, for me,, I am going to limit my shot to closer with a slower bow,,and if the bow is faster,, I may stretch it out a few yards, but like to keep the shots close for hunting,,, once it gets past 15 yards a deer can move quite a bit,, I like the closer shot with higher percentage of success,, :) I used to shoot a sinew bow 65# at 25 and it would shoot a 500 grain arrow close to 180 fps,, and even then at close range the deer would often be in a different position when the arrow got there,, I experienced this many times,, and was always amazed ,,,, so the older I got the closer I shot,, :)
JW,,,, I agree with you,, but if you make your shot closer ,, the heavy arrow is still going to be effective ,, there will be minimum drop to 15 yards,,
I agree the faster arrow does give you a slight advantage,,,,especially if you plan to shoot say out to 25 yards,, for me I feel like once you get to that range,, accuracy and deer movement can be an issue that even the lighter arrow can't compensate for,, I guess my point is , ,that the closer you shoot the less effect the arrow weight plays in taking the game,,, if both arrows shot great out of my bow it would be a toss up for me,, I would shoot the one that gave me the most consistent accuracy,,
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I think some are getting energy and momentum mixed up a bit. Energy out of a "system" should not change much but is dominated by velocity. Hence why velocity is squared.
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What you say makes sense, but isn't actually quite right.
Look at the graphs I plotted...
Yes energy out doesn't change much, once you have a heavy enough arrow
You'd think the velocity squared would dominate... but below that optimum weight. it doesn't!
Again see the graph... with the lightest bolt I got over 200fps, but the energy (and momentum) was far less than the heaviest arrow.
That's the whole point of doing all those tests and plotting the graph.... to see where common sense and intuition breaks down and and the actual performance of the system takes over.
The optimum is the arrow that is getting close to that maximum energy, whilst having the highest velocity, and thus most momentum, which is what I think you were alluding to.
Taking it to the limit, the arrow with zero mass is fastest, but it has no energy or momentum >:D
Del
Really, its whatever floats your boat, but in the fella's example of his two results momentum is higher with 770gr setup. And with all things being equal, will out penetrate high lighter setup. what many are not factoring in the fact is harder you hit a medium, the harder it hits back. The surface tension changes with velocity. That's just physics.
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Exactly JW. An arrow is a cutting tool that creates a channel the same way other ones do. There is negligible difference between temporary and permanent wound channels. There is little shock in the sense a bullet would give a prey. There is no conical wound expansion. There is no "takedown" power. A bow is not a gun, it's a bladed hole puncher. Every deer I've shot has been a through and through. You either hit the heart/lungs or you're going to be disappointed at one point or the other. Accuracy and speed. I can buy the cheapest hunting weight arrows I can and shoot it from my pse and as long as they don't explode upon release, I feel confident it will kill whatever animal you want if it's accurate. Because it shoots twice the speed of my trad bows.
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I think some are getting energy and momentum mixed up a bit. Energy out of a "system" should not change much but is dominated by velocity. Hence why velocity is squared.
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What you say makes sense, but isn't actually quite right.
Look at the graphs I plotted...
Yes energy out doesn't change much, once you have a heavy enough arrow
You'd think the velocity squared would dominate... but below that optimum weight. it doesn't!
Again see the graph... with the lightest bolt I got over 200fps, but the energy (and momentum) was far less than the heaviest arrow.
That's the whole point of doing all those tests and plotting the graph.... to see where common sense and intuition breaks down and and the actual performance of the system takes over.
The optimum is the arrow that is getting close to that maximum energy, whilst having the highest velocity, and thus most momentum, which is what I think you were alluding to.
Taking it to the limit, the arrow with zero mass is fastest, but it has no energy or momentum >:D
Del
Really, its whatever floats your boat, but in the fella's example of his two results momentum is higher with 770gr setup. And with all things being equal, will out penetrate high lighter setup. what many are not factoring in the fact is harder you hit a medium, the harder it hits back. The surface tension changes with velocity. That's just physics.
But there is no bow built that will cause an arrow to suffer from those effects. Hydrostatic shock is outa the realm of possibility even today, April 1st!
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I really like the physics part of the archery too--not so much that I want to go out and buy a chrono or chart force draw curve, or anything, but the intersection between theory and practice is great. Keep it coming.
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I love all the knowledge and ideas that get tossed around and shared here. My idea is using steel you'd want the bone crushing KE. Using obsidian that doesn't really matter so the optimum speed to weight would be ideal then
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Not saying anything about effectiveness of various weight arrows in hunting. Just what happens as the string accelerates with the arrow, here:
The speed of the limbs can limit the amount of energy transmitted to a light arrow because it accelerates faster than a heavy arrow, and receives less energy in the latter part of the travel in the bow. The faster the limbs, the less this is a factor.
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You guys got me going on this, Just ordered a chronny get it in a week , I was just thinking & wondering I would think every bow using wood is kind of unique to that paticular bow & bows like firearms have sweet spots for length & powder charge & such , so I guess my point is one size probably doesent fit all, some bows probably are more efficent with light arrows & some heavy ?
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Yeah, I think a bit of time making up a set of arrows from say 300 to 800 grain every 100grain should make for some interesting testing.
That's only 6 arrows but it should provide some good data. the hard thing is getting consistent chrony results. I've often toyed with the idea of making a shooting machine. it's not too difficult, but it would be one more thing cluttering up the garage.
Del
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Del, the kind of testing you are talking about where you use arrows from 200 grains to 800 grains is where you become keenly aware of "virtual mass"
Nearly all wood bows have quite a bit of hysterisis which is exaggerated by lighter arrows. I used to do a lot of testing but quit a couple of years ago. I came to the conclusion that if a bow holds the profile and has a decent design I will just take it out and see how far I can shoot it.
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Lite vs heavy can get vague sometimes as far as what heavy is.
Just my experience shooting, heavy or lite doesn't change much on targets or trees when hit out to 20 yards but 60-80 yards the heavy arrow wont stick enough to support their own weight. The lite ones out penetrate contrary to the ole heavy penetrates better way of thinking. I haven't tried extreme lite to compare. My best long range arrow weight for 50# self bow is 430g-480g with 125g tips with a foc around 13-14. 8-9 grains per pound. If hunting and short distance I may go on the heavy side, Maybe 10 gpp
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Tracker0721.....I like em all really.Something to be said for a softer initial draw bow too as far as accuracy goes,[swweeeeet]and as far as noise goes your heavier arrow will make less noise from your bow with things being equal here tillered properly wise.I know I've overshot deer and they spook closer to me for the next shot,,,,lol.You can be accurate with any weight arrow I think,if shot enough.At least with me it's that way.So many things go into this it's crazy.You got to figure these things out for yourself.Making your own equipment and testing gives you an advantage knowing in your gut what's what and what works no matter what the so called experts say.The common denominaters will be there.Welcome to the craze!!!!!!!!
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One thing too yet if it's field point penetration your talking about is that a 5/16" shaft will penetrate farther then a 23/64" shaft too.
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I think some are getting energy and momentum mixed up a bit. Energy out of a "system" should not change much but is dominated by velocity. Hence why velocity is squared.
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What you say makes sense, but isn't actually quite right.
Look at the graphs I plotted...
Yes energy out doesn't change much, once you have a heavy enough arrow
You'd think the velocity squared would dominate... but below that optimum weight. it doesn't!
Again see the graph... with the lightest bolt I got over 200fps, but the energy (and momentum) was far less than the heaviest arrow.
That's the whole point of doing all those tests and plotting the graph.... to see where common sense and intuition breaks down and and the actual performance of the system takes over.
The optimum is the arrow that is getting close to that maximum energy, whilst having the highest velocity, and thus most momentum, which is what I think you were alluding to.
Taking it to the limit, the arrow with zero mass is fastest, but it has no energy or momentum >:D
Del
Really, its whatever floats your boat, but in the fella's example of his two results momentum is higher with 770gr setup. And with all things being equal, will out penetrate high lighter setup. what many are not factoring in the fact is harder you hit a medium, the harder it hits back. The surface tension changes with velocity. That's just physics.
But there is no bow built that will cause an arrow to suffer from those effects. Hydrostatic shock is outa the realm of possibility even today, April 1st!
I don't believe hydrostatic shock is part of this equation. I am just talking pure momentum for an object to hit a medium. I myself have hit deer with a 420 arrow launched at 145fps that barely went into one lung. Maybe it hit a rib in a funny fashion, but also have seen an arrow so slow in flight, you think you could catch it, enter a deer and disappear, like going thru butter.
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if the deer is spinning out of the way,, penetration can be effected,, almost like you had bad arrow flight,, sometimes we don't pull the bow as far as we think we did in the heat of the moment( especially shooting down),,,,that will have an effect on penetration,,, sometimes our test or experience is biased,,, there is always someone that thinks the lighter arrow penetrates better, and that is their experience ,,I am sure it did on some particular test,,or could in some cases,, I like the shooting into water analogy ,,you can see very easy that the heavy fish arrow penetrates better,, and thats basically what happens when you shoot an animal,,it is great to explore the efficiency of the Primitive bow,,, different designs,, and see how far or fast they will shoot,,,,and in explaining what we think ,, we always learn something ,, or adjust our knowledge base as we learn something new,, :)
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I think some are getting energy and momentum mixed up a bit. Energy out of a "system" should not change much but is dominated by velocity. Hence why velocity is squared.
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What you say makes sense, but isn't actually quite right.
Look at the graphs I plotted...
Yes energy out doesn't change much, once you have a heavy enough arrow
You'd think the velocity squared would dominate... but below that optimum weight. it doesn't!
Again see the graph... with the lightest bolt I got over 200fps, but the energy (and momentum) was far less than the heaviest arrow.
That's the whole point of doing all those tests and plotting the graph.... to see where common sense and intuition breaks down and and the actual performance of the system takes over.
The optimum is the arrow that is getting close to that maximum energy, whilst having the highest velocity, and thus most momentum, which is what I think you were alluding to.
Taking it to the limit, the arrow with zero mass is fastest, but it has no energy or momentum >:D
Del
Really, its whatever floats your boat, but in the fella's example of his two results momentum is higher with 770gr setup. And with all things being equal, will out penetrate high lighter setup. what many are not factoring in the fact is harder you hit a medium, the harder it hits back. The surface tension changes with velocity. That's just physics.
But there is no bow built that will cause an arrow to suffer from those effects. Hydrostatic shock is outa the realm of possibility even today, April 1st!
I don't believe hydrostatic shock is part of this equation. I am just talking pure momentum for an object to hit a medium. I myself have hit deer with a 420 arrow launched at 145fps that barely went into one lung. Maybe it hit a rib in a funny fashion, but also have seen an arrow so slow in flight, you think you could catch it, enter a deer and disappear, like going thru butter.
Soooo many factors come into play on that shot that the list would bring the internet down! My first arrow into a deer was a 650 grain ash arrow moving about 140 fps, razor sharp two blade fixed broadhead....and the arrow was wagging back and forth from a bad release! It was wagging like a hungry dog watching a hotdog eating contest!!! I hit just behind the ribs in the paunch and didn't get good penetration. It taught me to not hunt with a bow until I had more control over the myriad of variables.
And so we argue back and forth, throwing out anecdotes and and science and opinion and experience. Hopefully, we all learn something and commit to MORE PRACTICE! Because no matter what your arrow choice, it is pointless (pun intended, this is me, remember?) if you are not capable of hitting vitals with overwhelming regularity!
Good hunting, folks!
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Just for the record.
I've just taken the trouble to go through my data and work out momentum for all the different weights. (It's allright, I don't expect any thanks ::) )
Momentum keeps increasing with arrow weight. (I was expecting there to be a peak somewhere :-[)
But there must come a point where although it has more momentum it is too slow to shoot accurately or indeed reach the target.
In my data, at the highest weight (approx 2000grain), the bolt was only travelling at about 40fps!
So it's up to the individual to find their own 'boat floating' trade off between speed/momentum/energy. ;D
Del
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thanks Del that is interesting,,,with wood arrows,, they will self limit,, you can only get so much weight per arrow,,
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Thanks Del, expected or not!
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This has probably already been said but I breezed through and thought I'd throw it out there. Kinetic energy=(.5)mv^2 momentum=mv. When calculating efficiency use energy, which should increase with arrow eight presumably because it increases the impulse. However momentum is the actual measurement of how much "motion" the arrow has and is directly related to penetration. Kinetic energy doesn't relate directly to penetration, the misconcetption that it dose leads archers to favor higher velocities (v^2) resulting in less than optimal penitration.
In short make your hunting arrows as heavy as you feel comfortable with.
(Apologies if I'm being redundant)
And I've noticed that y'all seam very interested in finding a happy ground between momentum and Kinetic energy, but unless your arrow is super sonic there is no reason to consider kinetic energy.
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My target doesn't seem to care much about penetration, so I'm interested in some other aspects of dynamics. A couple of them are the curve of the rate of acceleration of the arrow nock, and where in the firing cycle it reaches max velocity.
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its nice when the practical experience and the science of it validate each other,,its nice to know the whys,,,I am not good at the math, and it really helps how clearly you guys explain it,,,and hope the discussion helps others with their hunting set ups,, the speed is just a small part of it,,Tim Baker said " Let the measured speed of your arrow weigh the merits of your conjecturing.The arrow ,by the speed it chooses to fly,displays wisdom beyond Solmon's."
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I like that, BradSmith.
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I did a search of kinetic energy vs momentum and could't find a decent explanation of the difference in layman's terms. Then I found this which really addresses our issues and is funny!
A Thought Experiment:
Suppose that you were captured by an evil physicist who gave you the following choice:
You must either:
Stand in front of a 1000 kg truck moving at 1 m/s, or
Stand in front of a 1 kg meatball moving at 1000 m/s.
What's your choice?
Hopefully, you picked the truck! It's a big truck, but it is moving rather slowly (about walking speed), so assuming you don't fall down when it hits you (That would be bad...) the truck is just going to bump into you and move you out of the way.
On the other hand, you probably suspect intuitively that the meatball is a very dangerous object. It isn't that massive, but it is moving very fast (about 10 football fields per second) - and when it hits you it would do considerable damage to you, and keep going!
Consider the momentum and kinetic energy of the truck and the meatball:
Truck:
Truck's momentum = mv = (1000 kg)(1 m/s) = 1000 kg m/s
Truck's kinetic energy = 0.5 mv2 = (0.5)(1000 kg)(1 m/s)2 = 500 Joules
Meatball:
Meatball's momentum = mv = (1 kg)(1000 m/s) = 1000 kg m/s
Meatball's kinetic energy = 0.5 mv2 = (0.5)(1 kg)(1000 m/s)2 = 500 000 Joules
We know intuitively that the meatball is more dangerous than the truck, yet the momenta of the truck and the meatball are the same. On the other hand, the meatball has 1 000 times the kinetic energy of the truck! Clearly, momentum and kinetic energy tell different things about an object!
Del
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You can compare the energy using 1/2 m times v squared... don't worry about units as long as you are consistent.
So the 485gn at 162 fps gives 6364170 units of energy
The 770gn at 124fps gives 5919760 units of energy which is less, so I'd say you are going a bit too heavy at 770 gn as you are loosing speed and energy.
Del
Then divide by 450240 = Kinetic enrgy :)
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Your optimum spot is easy to find. The heaviest arrow will always be the slowest yet carry the most energy. You need to find an acceptable arrow weight for the game you are killing that is fast enough to be accurate with. Your 475 arrow is plenty heavy enough for deer and gives you good speed, I don't think I would want to go below 150 fps so if I were in your shoes I would choose something about 500 to 550 grains.
Bingo! I agree. Especially the part about "for the game you are killing..." I have put a fair share of venison in the freezer with arrows in the 475 -550 grain range, using bows from 45 to 55 pounds to know that they will do the job. If I am hunting big hogs or elk - 600 -650 grains is what I am shooting. I am no scientist, just a guy who spends way too much time building bows and arrows and then shooting those arrows into animals. If you are wanting an arrow to perform right for hunting it just needs a few qualities. It needs to fly straight and true. It needs to be quiet (heavier is usually quieter). It needs something damned sharp on the end. It needs to be fast enough to get there before the target runs off (too heavy and it is too slow). It needs to punch a deep enough hole to kill. This has been a fun thread and I appreciate all you learned folks that didn't shy away from higher math. :laugh:
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Easy. Do a simple penetration test to see which arrow is "better". If the heavier arrow, and you can accurately shoot it at the range you want, then you are done.
Regarding the energy thing, if you keep increasing the weight of your arrow then at some point the bow can't handle it, and it becomes pointless to use it. So the energy formula doesn't matter if the arrow only shoots 10 ft. You absorb more energy from the limbs with the heavier arrow, to a point. But it is "pointless" to to go beyond what ultimately results in an arrow that is not shootable at the ranges you want. If you want to shoot a heavier arrow, then build a bow that can deal with it.
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Now do you mean a more effiecent limb design Steve or a higher weight bow? What would the design need to exert more energy to the arrow and exert less on the limbs? Just wondering cause this has been mostly in regards to arrows but if I wanted a bow that shot heavier arrows better, is that possible? Like if I shoot 160fps with 400 whatever and 120fps with 700 whatever, is there a bow design that can get those numbers closer? Think it require an air bow to test though...
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Example: a pellet gun with a short power stroke of the same power will launch a heavier pellet slower then a light one but if you put a longer power stroke in it will launch the heavier pellet not as slow.
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Tracker no bow will shoot different weight arrows the same speed, lighter arrows will always be faster. Poorly made bows tend to benefit more from a heavier arrow but still perform poorly. Any 50# bow with a straight design will carry enough power to hunt successfully if it doesn't have excessive string follow or massive outer limbs. Just tiller the bow out carefully as to not damage the wood and keep your excess mass down in the limbs and you will be fine. Lots of perfect examples of styles posted here everyday you can reference.
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Yes, that's true.
I'm not sure why the need for it, but maybe somebody has one so I'm trying to think of an analogy to tracker's pellet gun with a longer stroke for a heavier projectile. I guess if you consciously short drew a lighter arrow than a heavier one, the speeds could be similar. And maybe if you had a second set of limb nocks the inners could be used for the heavier arrow. I dunno -- that seems something approximating the pellet gun example.
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Oh I'd hunt with a bow shooting only 100fps. That's plenty to kill a deer with a sharp broadhead. What I'm wondering is the most efficient. I know lighter arrows will always be faster but the more efficient the bow is the less the difference in FPS should be right?
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There's an argument that heavier mass limbs cast heavier mass arrows more efficiently than they do lighter arrows or than light mass limbs cast heavier arrows. I don't have a chronograph but I have similar weight bows that obviously cast heavy mass arrows better than others, way more than your 770's. Take a short bow, and a long bow, and change the tip weight and use the chronograph to see which combination gives the best performance with the heavy arrows.
Whoever said earlier here that the true flying arrow that is well placed is most important is way ahead. But not if the animal jumps out of its way. At 100 fps you better have a bow that is perfectly silent or plan to do a lot of blood tracking. Same with the ultra heavy arrows. Energy yes, but also slow, maybe too slow at the range you want.
You can't have everything from a 50 lbs. bow. All these formulas and theory only go so far in reality. They don't account for animal reaction, bow noise, or lethality--meaning, are you trying to kill a twitchy 150 lbs. whitetail deer or a 800 lbs. bull elk that is rutting hard? You might want that fast little arrow on the deer but that same arrow will bounce off the rib off an elk.
So in the end you have to know when you shoot your combo whether it will work. Does it go fast enough, penetrate enough, keep the noise down?
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Seems like an organized way to go about creating a dual purpose bow is to specify the two conditions that you want to achieve, rather than to try to generalize about it.
So let's say you want to shoot
1.) _________ weight arrow at _________ fps, and
2.) __________ weight arrow at ________ fps.
for a draw weight of ___________ and draw length of ________.
If you set those specs, then there may be a path to achieve that. Or a couple of different paths. Or maybe none if it truly is impractical.
But if we just talk about generalities, then the same things get repeated, and you really don't get a bow out of it. The most interesting thing is to work toward something real, and see what occurs as you approach that.
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the heavier the bow,, the better cast you will get from a heavy arrow,, and it will shoot a light arrow even faster, ,so if you want a dual purpose bow, shoot something like 70# @ 28,, then any arrow made from wood will work on any game,,, very dual purpose,, the lighter your bow, the more considerations goes into arrow weight and range of the shot,,, the heavy bow will do it all,, you just have to able to handle the weight,, and shoot it as accurately as needed for you application,,, this has not been mentioned I don't think, the heavy bows are not quite as efficient as the lighter bows,, a heavy arrow going 180 fps may take more draw weight than expected,, but its still going 180 fps,, so there is some trad off,, :)
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I did a search of kinetic energy vs momentum and could't find a decent explanation of the difference in layman's terms. Then I found this which really addresses our issues and is funny!
A Thought Experiment:
Suppose that you were captured by an evil physicist who gave you the following choice:
You must either:
Stand in front of a 1000 kg truck moving at 1 m/s, or
Stand in front of a 1 kg meatball moving at 1000 m/s.
What's your choice?
Hopefully, you picked the truck! It's a big truck, but it is moving rather slowly (about walking speed), so assuming you don't fall down when it hits you (That would be bad...) the truck is just going to bump into you and move you out of the way.
The question of how much an arrow will penetrate begins where your thought experiment ends, and for accuracy the two objects should have the same dimensions. After the collision the massive object will push you a hundred feet or so, but the less massive one is going to bounce off of your body (more so than the massive one).
Consider a .015kg projectile (about the mass of a soda can) moving at the speed of sound (340 m/s), and another identical projectile With the exception of its mass, which we will make .25kg ( less than 2/3 of the mass of a full can), moving at 83.3 m/s. both objects have the same kinetic energy (867 joules) but their momenta differ quite a lot (the more massive object has about 4x the momentum).
Now if we consider this as though we are actually shooting the cans, and you were hit with the lighter can you would get a nasty bruise and lacerations, as the can shatters against your body, and probably the air knocked out of you, but in the end you'd be pretty healthy.
But if it were the more massive object, you would be lucky to get away with a few broken ribs after being knocked back several feet.
Or you can make these objects about the size of a .22 and fire them into a wood block, you would find the more massive object penetrated about 4x as deep (assuming it doesn't shatter, etc.)
As far as distance is concerned, a faster arrow will always go further
Remember that momentum is literally a measurement of the quantity of motion, whereas kinetic energy is the capacity to do work.
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Thinking in a primitive way I cant help thinking theres so much more to this then just speed like caliber of the broad head , thats why some american Indian tribes adjusted there broad head size to the bows power (speed) & adjusting arrow flight so the momentum is in line with the broad head , at the end of the hunt its what works for you & your bow just a thought !
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i am nowhere near as skilled or mathematically edjumacated as the majority of you guys...
but...
the arrow your bow shoots most consistently and accurately coupled with the absolute sharpest broadhead you can hone on the pointy end is the best combo for hunting... a deer/elk/bear/squirrel/chicken doesn't know the difference between a 450g arrow @ 193fps or a 700gr arrow at 125fps... if you stick said arrow thru said aminals boiler room... it don't matter...
just my humble opinion...