Primitive Archer
Main Discussion Area => Bows => Topic started by: BowEd on September 07, 2016, 09:16:30 pm
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Say you got a bow that shoots pretty good for it's poundage.Now if that bow shoots a certain grain arrow at it's draw weight that's standard.50# bow shooting a 500 grain arrow @ 28" @ 150 fps.Now if that bow was to shoot a 700 grain arrow @ 28" @ 150 fps does that mean that bow shoots like a 70# bow then?
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I would say it shoots like a fast 50# bow. >:D
I see where you're going. I assume you mean a 70# bow of the same exact wood and same design as the 50#?
That gap in performance could be seen just from using better wood, a sinew backing, or an improved design I would think. Translating better performance into poundage leaves a lot of factors out I think.
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Isn't the 70 pound bow supposed to shoot 170? ;)
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I think a 70# bow that will shoot a 700 grain arrow 150 fps,, is about right, but I might be confused,, :)
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No, it just means your 50# bow has too much mass to make use of it's full potential
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I may have not explained my question right.Yes a 70# bow should shoot a 700 grain arrow @ 170 fps.That's standard.What I'm asking in a different way here is if this 50# bow shoots a 500 grain arrow @ 190 fps.What poundage is this 50# bow really shooting at?To me the bow is shooting 40 fps above standard.
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The way I understand it, a 50 lb bow shooting a 500 grain arrow at 190 fps is very efficient, so it is making the most of the draw weight it has compared to a less efficient 70 lb bow that might shoot the same arrow the same speed. It doesn't make the 70 lb bow any lighter at full draw; that bow just loses more of its energy on limb vibration or whatever. (Smarter people may want to elaborate on "limb vibration or whatever"...that's as technical as I get!)
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Excuse me this is @ a standard 28" draw also.
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Bows that shoot 170 fps @ 10 grains per pound regardless of weight are pretty common today. It has a lot to do with the shooter. Some guys will test very low with a good bow because they use a slower release method or creep away from full draw on release. I would guess that today most properly made self bows are shooting at about 165 fps if they are properly tested.
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Yes I too realize the bow is being efficient.All things being standard 10 gpp draw weight arrow @ 28" to start at here.What poundage is this efficient bow really performing like?If there is a formula or something to figure this out I'm just curious.My mind gets lost with figures floating around to figure this out.
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Yes form and release and speed can be different between individuals on the same bow.I'm along with that.What I'm asking is if this bow is shot by the same individual always.Anyway seems like another question for an engineer to figure out.
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A bow that draws 50#@28" is still a 50# bow whether it shoots a 500gr arrow at 150fps or 170fps.
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Yes but what poundage is that 50# bow performing at shooting the above standard speed of itself.
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I see.No one seems to know.Guess I come up with a real stumper to ask.Anyway here are my thoughts on my question.If a 50# bow is shooting a 10gpp draw weight arrow[500 grains] and it shoots that arrow at 190 fps.It cannot be performing like a 90# bow yet because the 90# bow is shooting a 900 grain arrow.If that 900 grain arrow is shot by the 50# bow it would not go as fast as the 90# bow's cast.I was thinking @ 150 fps then in comparison.Anyway I've read claims by bowyers of performances of different bows and was wondering what the thought process was to come up with certain figures.
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Ok, I'm going to try and take the scientific approach to this. In this scenario, like Marc said, the bow has too much mass for a 50 lb bow. The limbs can only move so fast with a given load. If the bow is shooting the same speed with with two different loads, then essentially the bow is at dry fire speed. With the lighter arrow, energy is being wasted, the energy has to go somewhere, this will be in the form of limb vibration and hand shock. This may be a terrible analogy, but put a piece of gravel in the back of a diesel pickup, and floor it, record acceleration, keep adding rock and eventually acceleration will start to slow at a noticeable rate, this will be your max efficiency. But when you add only a few lbs of rock, the pickup doesn't even notice it, just like you bow doesn't notice the added arrow weight. Too much engine for what your hauling. So with this bow, you would keep adding arrow weight until your arrow speed started to slow. To say the bow shoots like a 70 lb bow, sure, if you want to say that. It's hard to make that statement scientifically. Ideally, you would remove mass until the bow shot the 500 grain arrow at the point where any larger arrow would start to accelerate at a slower rate. This maybe hard without reducing any draw weight. Every bow is so different, each will have its optimum arrow weight to achieve max efficiently, all affected by design. BUT, I may be wrong on all this. Maybe someone can find some error in what I've said. Or maybe I've said too much....
Eric
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Yes but what poundage is that 50# bow performing at shooting the above standard speed of itself.
50 pounds. The bow is just approaching the capability of a 50 pound bow. Bows that shoot slower at 50 pounds are underperforming.
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OK I see then.Marc and you have misunderstood what I've said and asked.In order for a 50# bow @ 60" long to shoot a standard arrow 190 fps at a mass weight of the bow @ 17.40 ounces it is not over built.It is performing above standard.
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I guess the proper way of describing a bows'capabilities is to not compare it's speed to the above standard speed it is shooting then.There is no correspondance there.Just that it is shooting a certain fps above it's standard.
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The reason it is shooting the arrow @ 190 fps is because of it's lower mass weight and it's design.
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Beadman, I could be way off here but I thought you were asking if the velocity of the arrow say 700 grains, shot from the faster excellently built (whatever you want to call it) 50 pound bow, the one shooting far above average fps for a 50 pounder, is essentially the same velocity as your efficient, average 70 lb bow flung arrow of 700 grains. If I am way off sorry lol
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Yes.Then would you say the 50# bow shoots like a 70#'er?I'm not looking for praise here.I'm my own hardest critic and am wondering where the claims and correspondance is here.
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Or say this 50 # bow shoots a 650 grain arrow @ 165 fps then is it shooting like a 65# bow?Etc. like that with that type of correspondance.
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Well ok then.It's like I've stated then.A 50# bow shooting a 650 grain arrow @ 165 fps is performing like a 65# bow.Guess I answered the question myself.Sorry for the misunderstandings.We all have goals of various types and passions along with them too.
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Ed
I am not aware of a "formula" that can be cited to help you out, but you could easily do that with a piece of graph paper and bow testing with a chrony.
I am not suggesting that you undertake a survey and test project, but simply a way to record the specs of any bows that you make for your future reference.
If you plot velocity vs grains of arrow weight of a particular bow, yoiu should see a curve develop, that flattens on one end as the efficiency drops off. A bow with a different draw weight (but the same efficiency), plotted on the same piece of paper, will have a similar shaped curve alongside the first.
using the above example of plotting velocity vs arrow weight, will show differences of efficiency with differently shaped curves.
Plotting different metrics may give more easily comparable graphs. An possibility might be to plot grains/pound vs something else?
we often see force draw curves shown to "illustrate" a bows early draw weight and stacking, so why not a second curve to show how the energy is released?
willie
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Beadman, I think most of us understould the question fine. The problem with the question was that 150 fps was not a good place to start for comparision. You were starting at the bottom of performance levels instead of the average or closer to the top. If your 50# Bow shoots any arrow that a 70# bow shoots at the same speed it is performing as well as that particular 70# bow but it means nothing as some kind of standard.
When you talk about dry fire speed it is exactly that dry fire. There is no point at which lowering arrow weight will quit increasing speed. If you add or subtract about 7 grains from an arrow it will affect your speed about 1 fps. The lower you arrow weight goes the more effect reducing arrow weight has. If Take 100 grains away from a 500 grain arrow I will pick up about 15 fps. If I take away 100 grains from a 200 grain arrow I will add about 100 fps.
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Yes I hear ya willie.All I really realize is what has been said or read through no findings of my own.I don't understand the process completely.Any way a chrono tells a lot and it's enough for now.
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Ed
if a guy kept some force vs draw readings from when he tillered a bow, and then shot various weight arrows through a chrony when he shot it in...
he would have a notebook with some comparable data, for future reference.....
guess I do it on a piece of graph paper because it helps "visualize" the numbers.
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I see.Well I have a little better idea about this.I appreciate your insight.The standard I was referring to is 10gpp draw weight arrow and I think a 3 gpp draw weight string too.Bows are a trip that for sure.Into the dark groping around for answers.....lol.
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Yes.A draw weight check every inch.Resting maybe 5 seconds between draws.
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To me that seems like an awful lot of book keeping and testing for little gain. Keep that phrase for bragging. "Yup, 50#, shoots like a 70". I guess though,you might be able to use the data for other things. Carry on :D
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Here is a good way to look at it.
A 70# bow shoots 700 grains at 165 fps =42.27 KE
A 70# bow shoots a 700 grain arrow @ 150 fps= about 35# KE
A 50# bow shoots a 500 grain arrow at 175 fps=34 #KE
So the very fast 50# bow would be equal to the slow 70# bow.
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I see.Wonder what a 50# bow that shoots a 650 grain arrow at 165 fps is doing?Or same bow shooting a 450 grain arrow at 195 fps.Are these formulas in the TBB series somewhere????....lol.I should be able to figure this out myself.
It's not a matter of gain really to me it's understanding the process to see what is gained.A bow shooting with the comfort of a lighter weight bow but performing like a heavier bow is always desireable to me.The data gets turned into other things like a quicker kill and easier blood trail to follow.Not all exactly bragging type rights.Your taking my questions the wrong way.It's not just a target shooting type question.
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Beadman, message me your e mail and I will send you a link for a kinetic energy vs arrow speed calculator. When you are making comparisons always assume that the KE will go up slightly as arrow weights are increased. So a bow getting 35# with a 500 grain arrow will proably get 38# with a 700 grain arrow because they get more efficient with more grains per pound.
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Well I went on this sight called toughhead arrowheads.Findings from Dr Ashby's research.1/2 mass times velocity squared or KE=[1/2M] X [V squared].He gets into momentum formulas too.V=[M] X [V].All of the arrow itself.Penetration diagnosis is done then too.
He gets into it really.Seems like just tweaking the front of center on an arrowshaft can increase penetration.Using less and less feathers for a lighter back end.
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Yes there is a calculator there that tells me my KE & Momentum.
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Man yall are making my head hurt. ;) ;D ;D ;D
Pappy
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What I wonder is if momentum begins to matter more with massive sharp broadheads.. from reading their papers, it almost seems like momentum matters more. And mass even more.
toughhead... tuffhead?
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The data gets turned into other things like a quicker kill and easier blood trail to follow
Not trying to discount the bows poundage or the delivered FPS part of the equation, but when it comes to the arrows terminal effectiveness, I think that having a well tuned arrow, with some FOC, that delivers a straight-on impact, does as much for terminal performance as many of the other aspects under discussion.
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I knew about this tuffhead site too but did'nt realize they had a calculator right there too on the page.My mistake.Sorry Badger.
Dr. Ashby really gets into momentum being most important as far as penetration goes of broadheads Loon.I've got a friend here who's been shooting,tweaking,and experimenting with extreme FOC shafts all summer long and says everything that Dr. Ashby said is true.Arrows fly like a dart.Using just 2" feathers too I might add.They are set up almost like a javeline.African tribes knew of this long ago using very long shafts with no feathers and big tall above man size bows.
He will hunt with an extreme FOC shaft this fall to see.Gary is wanting 2 holes in deer to have an easier blood trail to follow and since it's only a thinner skinned deer he will use those shark tooth broadheads.For now I will just stick with my dogwoods....lol.
Getting a 40# bow to penetrate with a broadhead as far as a normal set up shaft shot from an 80 pound bow.These are all 20 yard and under shots too.Grizzly broadheads have the best mechanical bone busting advantage also.So it's just not the bow to be efficient.The arrow shaft is all important too.For hunting & penetration that is and other uses also I'm sure.Hard to believe I know.If anyone is interested I suggest to read Dr. Ahsbys' findings.He is thorough.He tested on slain buffalo within 6 hours of being slain.
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You bet willie.Your on point there.
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Seems like the discussion has drifted to arrow shafts...lol.,but still an efficient bow used is all important along with a properly set up shaft.I am in no doubt that 90% of the deer hunters out there are not using this advantage to hunt with.
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my experience with extreme FOC has been that they do not yaw as bad, and consequently can get by with less fletching, but there is a tradeoff with the extreme FOC not shooting as flat a trajectory. Good flight can be had with not so extreme FOC , if you have trouble re-adjusting your range estimation, but a little more tuning is often necessary. Of course we do that with center balanced arrows anyways. There are also some arrow manufacturers spewing BS about extreme FOC giving extra range....
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ok I thought about it,, yes a 50# bow shooting a 700 grain arrow 150fps is shooting the same as a 70# bow shooting a 700 grain arrow 150 fps,, :)
in the first Bowers Bible Tim says a normal 70# bow should shoot a 500 grain arrow about 177 fps,,we didnt do much 10gpp back then,the first mojam stats are all 500 grain arrow,,
I know things have changed a bit since then,, but in my mind,, that is still an ok shooting bow,,today we would expect it to shoot a 700 grain arrow 165 fps,, ???
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haha that is so slow wat, there's 50 pound bows that can shoot a 500 grain arrow at 180fps...
But I guess it'd still get the job done, I'd hate having to yank back 70# just for that though. And it's probably better to have a more accurate bow than a really fast one when hunting... I think accuracy and having the arrow hit straight are most important?
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my experience with extreme FOC has been that they do not yaw as bad, and consequently can get by with less fletching, but there is a tradeoff with the extreme FOC not shooting as flat a trajectory. Good flight can be had with not so extreme FOC , if you have trouble re-adjusting your range estimation, but a little more tuning is often necessary. Of course we do that with center balanced arrows anyways. There are also some arrow manufacturers spewing BS about extreme FOC giving extra range....
Extreme FOC will not change the trajectory anymore than just adding the same amount of weight anywhere on the arrow.
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Loon...With 20 yard shots the force of momentum by a 650 or 700 grain arrow for penetration is a bit farther than a 500 grain arrow.Even though it may be going slower.It gets pretty technical that's for sure.The calculator shows it.Just some really good food for thought and understanding.The analogy was explained like this.Throw a plastic wiffle ball then throw a baseball.Which one's gonna leave the bigger mark?Kind of extreme but I think as the speed ramps up the difference gets greater with arrow shafts.Seeing impact with a slow motion camera I'm sure would reveal that the extreme FOC shaft being lighter weight in the back 2/3rd's of the shaft would'nt experience the reverse paradox that a center balanced shaft would experience.That energy on the FOC shaft would go or stay forward for better penetration.These shafts have to fly as good without feathers as with also of course.Accuracy is pretty much a given with all of this.
willie.....My friend Gary had to go to very lightweight carbides to get his 32% FOC on his shafts.350 grains on the tip on a 636 grain arrow.Which Dr. Ashby found to be close to the overall weight that did the best.It can be done with wooden ones too,but not quite as high a percentage.Personally if I was to get after it I would use spruce first thought off hand.Stiff and light weight.Foot it[purple heart or hedge] with a heavy tip and taper it to the nock.Gary said all he did to minor adjust elevation flight was twist his string a time or two to move his string nock.That is'nt much.There's all kinds of BS sales pitches out there.Biggest one is this rage chisel tip butterfly broadhead.Junk!!!I'm very glad to read that with all the testing Dr. Ashby did he found the 2 blade broad head to be the best for penetration.Makes sense.
Brad....My other friend Grant has told me more than once his son killed his first deer with a 35# bow.Don't know if that was legal in Iowa you know but I know the guy and he does'nt lie.So just to kill a deer does'nt take a whole lot if in the right spot.With your elk hunting now going on that's a different story.I sure hope you can get within range of one.These two guys I mentioned have both shot elk out west and many times lately just can't get closer than 50 yards to them.Your first encounter was a biggie I'd say.The other fella with us on 3D shoots Ed has shot 13 elk out west.All with a long bow.
All this info is just out there you know.It's interesting to me.All of the info that Dr. Ashby found over years and years of testing he did with his own money,and did'nt take a dime from the company that approached him.These tuffhead people.He's a phycisist himself.Talk about passing it on heh....lol.
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thanks Ed, I have lots of" theories" certain set ups are proven over and over, so I put alot of weight on what has worked,, and try to keep an open mind for improvement,, I am lucky to have "Tested" some set ups in real hunting situations, and seen others first hand using the long bow in successful and not so successful applications,, most under estimate the effeciencly of heavy arrow and two blade,, you just have to see it work to really get it,, it can become complicated on paper,,,
I made an arrow for a friend for a buffalo hunt,, it weighed about 1000 grains,,,,,2 blade broad head, the bow was osage, b 50 string, average,, probably shooting a 500 grain arrow 165 fps,, not sure what the 1000 grain was doing,,
his shot was about 30 yards, off horse back, the arrow came out the other side,, some would say 165 fps with 500 is very slow,, and it might be compared to some bows,, but in a hunting situation, the end results are really telling,, in this situation the broad head and the weight of the arrow got the most out of the cast of the bow,, later he told me the arrow hit a bit lower than he was aiming,, I guess so :),,that hunt was filmed,, the arrow was in perfect conditon ,, just a little blood on it,,
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Wow that's wild to blow through a buffalo.. Really enjoyed reading some of Ashby's papers. It is good to know some of the actual reasons why/how the FOC is important. May affect the way I make some of my arrows these next few weeks
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Yea you guys it's just food for thought you know.Understanding things.Im in no way close to an engineer or physicist but do respect their findings.More so than promotional sales pitches from companies.Actual usage like you said tells it to ya.That means more shooting and bow making and more arrow making....lol.A good bow for hunting is important but equally and even more so the way the arrow is set up too.Target shooting too.Where it all begins for testing.
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After further looking at Dr. Ashbys' info and videos he's proven by demonstrations the eyes can see that an arrow even 20% heavier will fly farther with at least 32% FOC.Because of the lessened paradox the extreme FOC shaft experiences recovering quicker from leaving the bow.Problem lies in that to get that percentage of FOC in natural material wood shafts is pretty hard to do in primitive archery.Carbides allow it to be done a lot easier.I can get it with shoot shafts with a heavy tip into the 20%'s FOC balanced but that's about it.Still noticeable though.Normal balanced shafts are around 10% at best.I'd have to try my idea of bare shaft tuned spruce shafts footed with heavy tips and with 2" feathers.Because of the extra weight up front the spine needs to be increased to handle that.All this will get a normal shooting bow to be more lethal and a more efficient bow to be more lethal yet.All of this one may say does not conform to primitive archery.Not so.The tribes in New Guinea figured this out with their bows and arrows.Through trial and error I imagine.
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an arrow even 20% heavier will fly farther with at least 32% FOC.Because of the lessened paradox the extreme FOC shaft experiences recovering quicker from leaving the bow
interesting, could you supply a link to where those observations about arrow flight were made?
I must have got sidetracked in my recent Ashby reading. Did see quite a bit about FOC relating to penetration though, but that's a different subject.
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Yes.It's on the same tuffhead site.I'll get back here in abit to tell ya.
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Go to tuffhead site.On the left hand side click on Ashby May 2013 Dallas Texas.Go to video number 4.
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Ed
checked out that video, and I wish that we could see the flight of the arrows better in the flight test where he is making that claim.
He can demonstrate more range with heavier arrows because the extra weight and extreme FOC adjusts the dynamic spine of his straw to his bow. His demonstration is comparing apples and oranges because the lighter straw is grossly overspined and just shoots terrible.
ashbys claims for better penetration with more FOC seem more well founded to me, as bradsmith has demonstrated.
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Yes the heavier straws' spine may have been softened to fly straighter.While the lighter straws spine made it shoot at more of an angle.I see your point.Maybe somewhere he does shoot real arrows to prove his point.The jury is still out in my book about this yet.