Primitive Archer
Main Discussion Area => Bows => Topic started by: sleek on April 22, 2018, 09:39:42 pm
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I have an issue with the 10 grains per pound and feel if this were fixed, all bows would compare equally in performance without the longer draw length people taking the advantage of shorter. We need to change the standard.
I wrote this back in 2012 and i still feel this way. If I can make Any contribution to archery, i want this to be it.
I would like to express an opinion based of things I understand to be true and things I have read that others believe to be true. I am asking only to raise more questions, not present facts.
I think that the idea of shooting a 10 grain per pound arrow is a bad one. I think it can be misleading and overload or underload a bow depending on the bows powerstroke ( draw length minus brace heigth ). My point is bassed off stored energy. To start off with an example, I will use the cross bow. A cross bow may have a 14 inch draw and a 200 lb draw weight. ( not listing numers from any specific bow, just numbers that could be. ) If this bow were to shoot a 10 gpp ( grain per pound ) arrow it would fire a 2000 grain arrow. That arrow would fly about as far as a brick.
What is the reason for this? I feel the first answer is so obvious you would wonder at my question, but the answer is more detailed than the obvious " the arrow is too heavy " answer one would be likely to spurt out at first thought. I would be more inclined to say that the poor flight of an arrow 2000 grains out of a 200 lb @ 14 inches bow could be blamed on the arrow not being correct to the ratio of power stroke to draw length. The distance a bow is pulled in combination with the weight it reaches ( see note below ) will determine how much energy the bow stores. In this argument assume a well built bow with low tip mass, set, ect... This energy storage is all the bow has to offer to the arrow.
If you always make the arrow 10gpp, the shorter power stroke bow will suffer because of the reduced energy presented to it compared to that of a longer powerstroke bow. I would venture so far as to say that a 50 lb @ 15 with 10 gpp would perform less in arrow flight than would a 30lb @ 30 inches with a 500 grain arrow from the 50 lb bow. ( I havent done the math, but I used the numbers to illustrate my point. )
There must be a ratio of energy storage of the bow to grains per pound of arrow mass. The idea of having a standard by which to measure a bows performance is good and needed, but I think I have shown why I think 10 gpp is a bad way to measure performance of a bow, just as bad and flawed in the same way as ( those who have read the TBB series will remember this one ) measuring all bows performance with a 500 grain arrow regardless to poundage or draw length. These two factors must be calculated into measuring a bows performance. And since it is draw weight and length the bow offers ( potential energy ) and weight of the arrow I think a ratio should be calculated and used to determine the effeciency of a bow based on draw length, weight and arrow weight.
As an additional thought to this topic, I think there is a maximun effecient draw length for every draw weight of bow and that will depend on the arrow weight chosen. Shorter draw lengths get lighter arrows, longer draws get heavier. But again, here I say there is a ratio.
( Ref. note above )
The end poundage of a bow does not matter as much to the kenetic energy of an arrow as does what the force draw ( FD ) curve looks like. High energy storage in a bows early stages of draw gives the arrow the benifit of the rest of the draw length to absorb that energy. The longer the arrow is inside the fat of of the FD curve, the happier it is, as an arrow can soak up energy as fast as it is given. The more energyin the FD curve that is ahead of the arrow ( read early draw weight ), the more it leaves the bow with. This was not exactly part of my original discussion but felt it played a significant part of the performance of a bow and needed to be understood by people who havent read about fd curves yet.
After presenting my argument, Dave, aka woodbear, came up with this simple formula and I believe its the one that should always be used.
10gpp x draw/28
This little gem can normalize any draw length and put every bow on an even playing field by adjusting the arrow weight to the bkws draw weight AND draw length. I bring this up every chance i get. I feel like if this oportunity to adopt this formula as a standard is wasted, progress will NEVER be made.
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Interesting, very. I need to keep better notes. doing my own penetration tests, I could see that the reality overtook the 10gpp rule.
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Its been the standard for a lot of years I have a longer draw ,I always post chrono numbers with 11 gpp arrow and only post numbers after the bow has been shot in 300 arrows & strung for 1 hour and 12 arrows shot before chrono, I want to know what the bow really does in real world conditions if I would shoot some of the bows fresh I could say its doing 192 fps but after 300 arows and strung for 1 hour 12 arrows prior it ends up being a 178 fps bow ! My point is there is a certain amount of comon sense that goes into all published numbers !
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"standard"
"Always"
For pities sake gents ::)
Remember our roots... did the native Americans, neolithic man or the English Yeoman at Agincour* follow the "rules"?
Ok, 10 gpp is a reasonable guide for most normal situations...
But is this forum really about the normal or is it about the different, the exceptional and the practical realities ?
Get grip! ;)
Del
* actually there was some standardisation and mass production of bows and arrows for the 100yrs war, but I don't think the arrows conformed to 10gpp * ;D
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Sleek, I think the 10 gpp figure is often cited so that at least one variable can be held constant when comparing the performance of two different bows. That is all the 10 gpp figure is for. No one is saying everyone should always shoot with arrows that weigh 10 gpp.
The method you are suggesting would effectively invite us to compare the performance of two different bows by holding nothing constant. What is the point of making the comparison, then?
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I'm with Del and Eric. On the other hand if you don't follow the rules set by the ole timers the earth will fly out of orbit and kill us all.
I find similar "rules" in all of the crafts and or skills I've dabbled in over the years. And almost always it goes back to what Erick said, it was originally a rule of thumb or basic guideline that eventually turned into a hard rule.
And I believe the reason these standards turn into unbreakable rules that must be adhered to is people loose sight of why they came about.
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I have used Sleeks method for years when testing longer or shorter draw bows. I mainly use it to keep efficiency figures consistent. One of the main reasons I am against it in a flight shoot is that we are attempting to build a kit with a set of rules and protocol that can be passed from shoot to shoot anywhere in the country and they will all be stored in the same data file and are competing for the same records. 28" was chosen because it is the most common draw length bows are built to and 10 grains per pound is easy enough to compute and is also a well accepted number used by hunters.
In scenario like this I believe the shorter draw bows would start having an advantage unique to self bows. In the later inches of draw is where we enter what I call the death zone where bows start to pick up set and hysteresis. It is a credit to the bowyer that he can get his bow out to the full 28" draw and still maintain the same high level of efficiency that he had at 24". The vast majority of bows start falling off once they go past 24".
I would be all in favor of the chrono test being run Sleeks way except for one reason. I was hoping we could use the chrono test to compare speed against distances so that bow makers working and testing at home with hopes of breaking existing records would be able to use their chrono to find out if they were in that record range or not.
I actually have several reasons that are not arbitrary as to why I chose the 10 grains at 28". I am very aware of Sleeks method and use it myself in testing but I just don't like it for this particular type of event. For regular flight shooting where light arrows are used of any length it is an entirely different matter.
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I think the 10 gpp is a suggested arrow weight for hunting arrows
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In testing arrow speed, 10 gpp is a good thing. It means you can vary everything but the weight of the arrow draw length and the draw weight in your effort to get speed. The only measure is speed.
You can make shorter limbs, lower mass, radical limb shape and whatever you want. The measure of your efforts is the speed of the arrow.
Doing otherwise is like handing out blue ribbons for particiation.
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" In scenario like this I believe the shorter draw bows would start having an advantage unique to self bows. In the later inches of draw is where we enter what I call the death zone where bows start to pick up set and hysteresis. It is a credit to the bowyer that he can get his bow out to the full 28" draw and still maintain the same high level of efficiency that he had at 24". The vast majority of bows start falling off once they go past 24".
Confirmation bias at work.
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This is not confirmation bias at all, on the contrary it is an area I have spent considerable time testing out. We know for a fact now that set not only contributes to loss of performance due to loosing profile but also due to increased Hysteresis. It is well documented that bows are more prone to set the further we draw them. Your last comment was out of line and not qualified. Shorter drawn bows given a handicap based on stored energy would have a distinct advantage.
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Intriguing post Badger. Do you think that might be why the average Native bow was around 55 inches, and many Natives snap-shot with shorter draw lengths? Might they have gravitated towards those size bows and that style of shooting to minimize set, reduce hysteresis, and optimize efficiency?
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Intriguing post Badger. Do you think that might be why the average Native bow was around 55 inches, and many Natives snap-shot with shorter draw lengths? Might they have gravitated towards those size bows and that style of shooting to minimize set, reduce hysteresis, and optimize efficiency?
I am almost certain that's why they built them that way. When I get back I will give you a real life example done at an official test contest we used to have.
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This is not confirmation bias at all, on the contrary it is an area I have spent considerable time testing out. We know for a fact now that set not only contributes to loss of performance due to loosing profile but also due to increased Hysteresis. It is well documented that bows are more prone to set the further we draw them. Your last comment was out of line and not qualified. Shorter drawn bows given a handicap based on stored energy would have a distinct advantage.
The bow may have an advantage due to hysterisis but that is probably negated with the longer draw length adding to the power stroke
I think 10 GPP is a good common denominator.
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I was going to give a real life example of a test that was done publicly. In 2008 we held a walk the talk event which was open to all kinds of bows both modern and primitive. I had a bow that was doing particularly well at home drawing 24" and I chose to leave it there to demonstrate short draw capabilities. At 24" draw and 10 grains per pound it was shooting at 175 fps. About the fastest I had ever gotten at 24". Using the Woodbear stored energy method shooting a 428 grain arrow it was hitting 186. When it came time for the formal test there were a lot of bows in line and it was too much trouble to readjust the shooting machine for 24" so I told them to just shoot the bow at 28" after a series of pulls to seat the bow in. At 28" and 10 grains per pound the bow was now shooting at 176 I believe. 9 fps below what the equivalent arrow weight was hitting at 24" draw.
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Badger, are you saying that all bows shoot better at 24 than at 28 with a 10 gpp arrow? Seems to me a longer bow would fare better at 28, for example an elb.
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Sleek, I think the 10 gpp figure is often cited so that at least one variable can be held constant when comparing the performance of two different bows. That is all the 10 gpp figure is for. No one is saying everyone should always shoot with arrows that weigh 10 gpp.
The method you are suggesting would effectively invite us to compare the performance of two different bows by holding nothing constant. What is the point of making the comparison, then?
Actually, in this equation 28 inches IS the constant. It allows all draw lengths to be compared to a 28 inch draw, regardless if draw weight and length. It is far from NOTHING being a constant. By deffinition, the equation HAS a constant. I dont think you understand the math there and the point of my argument.
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Sleek, at 10 grains per pound the 28 inch draw has an advantage over the shorter draws but using the handicap the shorter draw bows would gain an advantage over the 28" draw bows. A very significant advanatge in some cases. Also shorter arrows seem to fly further.
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Badger, what do you think the reasoning for your bow shooting after at 24"? Maybe you already explained it, but I missed it. It's very interesting. It does seem that there would be an optimum arrow weight for each individual bow based on tiller and profile.
I get what sleek is getting at, but it seems there are far more variables. You could tiller a bow to shoot light arrow for its poundage, or design to shoot heavy for its draw weight. How the bow is "geared". Isn't that like comparing a diesel truck to a dragster? Both have 700 horses, but neither can do the job of the other. Ignore me if I'm way off here.
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I guess if my goal were to be to build a bow that shoots a 10 gpp arrow the fastest, id build a bow to that purpose, and take draw lenth into account. If thats the only goal. No complaints there.
If the goal is to put all bows in a level playing field, where midgets can run against giants in a fair equal foot race, the field needs to be adjusted accordingly. Then its a fair compareisin in all bows to eachother, and not to a specific purpose or task.
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Badger, what do you think the reasoning for your bow shooting after at 24"? Maybe you already explained it, but I missed it. It's very interesting. It does seem that there would be an optimum arrow weight for each individual bow based on tiller and profile.
I get what sleek is getting at, but it seems there are far more variables. You could tiller a bow to shoot light arrow for its poundage, or design to shoot heavy for its draw weight. How the bow is "geared". Isn't that like comparing a diesel truck to a dragster? Both have 700 horses, but neither can do the job of the other. Ignore me if I'm way off here.
In this case it wasn't gearing. It was simply the bow took on more set and hysteresis after being drawn out further. This will be true to some extent in nearly all bows. Hysteresis is a major loss in wood bows. The last few years around here I have seen a huge improvement in how well the bows are holding their profiles, I am also seeing a big jump in reported speeds these same bows are shooting. The bow I am talking about if I went back to drawing it at 24" would not have anywhere near the speed it had before being drawn out to 28". It was now a 28" draw bow and would be a dud at 24" from that point on.
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I was going to give a real life example of a test that was done publicly. In 2008 we held a walk the talk event which was open to all kinds of bows both modern and primitive. I had a bow that was doing particularly well at home drawing 24" and I chose to leave it there to demonstrate short draw capabilities. At 24" draw and 10 grains per pound it was shooting at 175 fps. About the fastest I had ever gotten at 24". Using the Woodbear stored energy method shooting a 428 grain arrow it was hitting 186. When it came time for the formal test there were a lot of bows in line and it was too much trouble to readjust the shooting machine for 24" so I told them to just shoot the bow at 28" after a series of pulls to seat the bow in. At 28" and 10 grains per pound the bow was now shooting at 176 I believe. 9 fps below what the equivalent arrow weight was hitting at 24" draw.
That is fascinating. I am editing up our conversation for my podcast, and just listened to both of us talking about how we have been preferring longer bows as of late. Now you are making me want to revisit shorter bows and polish up my snap draw.
What were the dimensions of the bow you tested? Length, draw weight at 24 and 28 inches?
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Eric I had built 4 bows that were bamboo backed osage and almost twins. They went from 65 to 67" overall length and were reflex deflex designs in the low 50's. I think they were built with about 2 1/2" reflex. One was tillered to 24" one 26" and two at 28". One of the 28's broke during the test. I gave the 26" away without testing.
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i should have added that this bow was tillered for a shorter bending area than a 28" draw would need, a little luxury shorter draw bows can enjoy.
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So, for the sake of clarity, one of the 65-67 inch bows was tillered to 50 lbs at 24 inches, one was tillered to 50 @ 26, and two were tillered to 50 @ 28? So draw weight was constant at the different draw lengths?
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So, for the sake of clarity, one of the 65-67 inch bows was tillered to 50 lbs at 24 inches, one was tillered to 50 @ 26, and two were tillered to 50 @ 28? So draw weight was constant at the different draw lengths?
, They were very close in the low 50's and were tested with corresponding arrows. The 24" I had tested more at home because I was intrigued with its short draw speed.
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5
10gpp x draw/28
Can someone explain how to use this. What is the 5 doing up there?
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Typo, fat fingers, small keyboard. Sorry.
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Thanks. I tend to short draw a bit so it looks like I should be shooting 9 gpp.
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I dont think there is a problem with the 10 gpp rule its just one factor the problem with chrono numbers is they can easely be skewd most self bows will shoot 5-15 fps on average faster when fresh, I have done a lot of testing on that & posted ,and other guys here to , and leaving a bow strung for 1 hr & pre shooting a bow before testing even more loss , after about 300 arrows things seem to stabelise in my testing ,so my point is it would be dishonest for me to post fresh numbers that would do nobody any good especialy my self wanting to know what a design will really do in the real world I think hunters tend to want real world numbers setting in a stand or blind for hours can change a bow ! sinew & laminate bows seem to be less effected by it in my testing ! Not scientific but practical tests.
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Thank you very much for bringing up this topic, sleek! Itīs a very interesting one.
For chosing the right arrow weight, you have to ask yourself what you are using them for. Is it for hunting, target archery or flight archery? What distances are you shooting at? Do you want to have the quickest arrow flight possible or not? Your equipment (bow and arrow) must be adapted and tuned to each purpose. So I think that only comparing quite simular bows using the same draw weight and draw lengh will give you meaningful results which you can compare to each other.
Let me show you this hypothetical example for clarity:
Letīs say we have two different historical examples of composite warbows with the same draw weight (letīs say 130 lbs).
1: ottoman bow, 42" lenght, 130 lbs @ 27", mass: 14 ounces
2: manchu bow, 70" lenght, 130 lbs @ 32", mass: 32 ounces
Both bows are tested with a very light 450 gn arrow (3,46 ggp) a typical arrow weight for ottoman war bows.
The ottoman bow will easiliy outperform the manchu bow, because of the very low mass of the bow.
After that, both bows are tested with a heavy 1500 gn arrow (11,54 ggp), which was a typical arrow weight for manchu war bows.
The manchu bow will easily outperform the ottoman bow, because it stores a lot more energy due to its length, longer draw length, strong reflex and its long sharp angled syhas.
Testing different bows only with one arrow weight could lead to false conclutions about their performance. Itīs like comparing apples to pears. In order to see the real potential of a bow design, you have to test it with an arrow weight matching the bow design. Bearing that in mind, you can say that both the ottoman and manchu bow were excellent designs for their own arrow weight and purpose.
But of cause you can much better compare two bows of the same design with similar parameters.
Greetings, lonbow
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Nice post Lonbow :)
Del
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Ah yes, "Matching bows to arrows." Dean Torges wrote an article about it. It's on his website.
"I guess if my goal were to be to build a bow that shoots a 10 gpp arrow the fastest, id build a bow to that purpose, and take draw lenth into account. If thats the only goal. No complaints there.
If the goal is to put all bows in a level playing field, where midgets can run against giants in a fair equal foot race, the field needs to be adjusted accordingly. Then its a fair compareisin in all bows to eachother, and not to a specific purpose or task."
I agree, Sleek.
I don't care about that race, or any formula that would attempt to integrate and level those fields. I DO I have specific purposes for my bows, but have found the numbers I need to build them on a tape measure.
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Me too squirrels. My bows are made to hunt with so balance and noise are my only real worries. If I were to make lng distance bows I would worry more about speed. To me if it shoots where I'm looking in twenty yards What does it really matter that my arrow weighs 10gpp if 5 gpp does as well in that range. In fact lighter arrows would be faster to the animal which should make more accurate shots. Sound right?
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Me too squirrels. My bows are made to hunt with so balance and noise are my only real worries. If I were to make lng distance bows I would worry more about speed. To me if it shoots where I'm looking in twenty yards What does it really matter that my arrow weighs 10gpp if 5 gpp does as well in that range. In fact lighter arrows would be faster to the animal which should make more accurate shots. Sound right?
A broadhead flight shoot is not about distance flight bows, it is about hunting bows shooting hunting weight arrows. It is just verifying the cast
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I think of the collagen in a bow as only being able to stretch eversoslightly before it loses tension (takes set) so naturally a bow only drawn to 24 inches would have more snap than a bow drawn to 28. But due to the shorter draw there is only so much overall energy available to the arrow. The longer bow could drive the same weight arrow better because of the longer stroke but I has lost efficiency because it has stretched more than the fibers should. Am I getting this right badger?
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The fibers compress rather than stretch and they are not collagen.
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I think of the collagen in a bow as only being able to stretch eversoslightly before it loses tension (takes set) so naturally a bow only drawn to 24 inches would have more snap than a bow drawn to 28. But due to the shorter draw there is only so much overall energy available to the arrow. The longer bow could drive the same weight arrow better because of the longer stroke but I has lost efficiency because it has stretched more than the fibers should. Am I getting this right badger?
Pretty close, it is mainly in compression where the efficiency is lost
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Maybe we need a bigger playing field! See ya at the flats.
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This conversation with Sleek in Badgers thread seems better off moved here.
. I personally don't feel there is a good way to even the playing field by using a set formula to adjust weight. Lots of variables that doesn't allow for.
There can be a difference between a formula of "what is supposed to be", and a formula derived from actual shooting stats.
Different styles of bows will have different types of fdc's. I doubt a perfect formula for this really exists.
I think we agree a perfect formula does not exist. A process derived from actual stats would not be a formula in the classical sense. "Formula" was a poor choice of words, I am suggesting something more like a correction factor. A perfect formula would be an attempt to predict how a bow should shoot, correction factors would be more about how a variety of bows styles and construction, arrows lengths, arrow weights, drawlengths etc. have shot in the past, the factors being developed as records are kept. A way to equalize various concerns about how "level" the field is going forward. Moving the goalposts, as some might say, could be a way to shoot with a broader range of arrows without having to develop and define lots of rules and create numerous classes.
You seem to want to make a flight bow compare with a hunting bow ( as an exaple you didnt give).
Sleek, I am thinking of a way to broaden the arrow weight and drawlength specs, but stiil stay well with in the realm of Steves proposed hunting broad head round.
Something that might include 90% of what guys hunt with. A rough example might be 26" to 30" draws and 8gpp to 12gpp. It would let a guy shoot what he has developed as his best hunting set up. It would be a shame if you could not compete with the arrow you like to shoot with your bow/drawlength.
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I too have the impression that short draw bows can be made to shoot a bit faster, that is, with Woodbear's formula that allows for lighter arrows at shorter draws.
There is obviously a trade-off between length of the power stroke and energy returns.
At 24" draw there is less energy storage than at 28", nobody argues about this. But also less hysteresis. For hunting purposes (or warfare for that matter) penetration damage is crucial. A longer draw will store more energy, and allow a heavy arrow to penetrate further. At the expense of taking a bit more set. The extra 4" draw doesn't pay off as much as the previous 4", but enough to tip the balance in favour of more power and energy storage (and efficiency).
For flight shooting, a short draw with lighter arrows (which incidentally also oscillate at higher frequencies, and therefore stop wobbling faster) is more advantageous than a long draw. Raw energy storage is less of an issue, with light arrows efficiency (the energy put into the cast divided by the energy stored in the draw) hardly matters. Raw speed is what matters (next to arrow-bow and release tuning).
But don't go comparing (as the last questions to Badger) a bow made to shoot 28" but only drawn at 24" to a same design bow shot at 28".
I think Badger's point is that a 24" draw bow isn't necessarily slower than an 28" bow. And because care is taken (in his case) to hysteresis and set, his bows stay fresh more easily when limited to 24" ,than when drawn to 28".
As for the short bows: they have less inertia, so a little excess mass at the extremities is less of an issue than in long bows. Making a long bow (67" or more) and shoot it at 24" and being very fast requires utmost attention to mass reduction in the lower limbs.