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  #1  
Old 07-30-2020, 05:36 AM
Tracker1 Tracker1 is offline
 
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Default Poundage FPS

Is there any formula or idea of how many FPS you pick up per pound on a 550grn arrow from a recurve?
Iím trying to get the most out of my Samick Sage for hunting.
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  #2  
Old 07-30-2020, 05:53 AM
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stoutstuff stoutstuff is offline
 
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Default Re: Poundage FPS

3Rivers "Dynamic Spine Calculator" should get you close.
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  #3  
Old 07-30-2020, 07:00 AM
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Default Re: Poundage FPS

Depending on what you're comparing to, you might loose.

Bowmania
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  #4  
Old 07-30-2020, 07:56 AM
pavan pavan is offline
 
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Default Re: Poundage FPS

Remember that lighter draw bows can have a greater efficiency than heavier bows. More cast in grains per pound. However, different design bows vary in efficiency also with different draw weights and draw lengths. Some bows do not lose as much cast with shorter draw lengths, not gain as much efficiency with longer draw lengths. While other bows can have a dramatic drop in performance at shorter draw lengths and arrow changes. Some bows gain a bit of performance when the bow is shortened, while other are more efficient at longer lengths, that depends on design and tiller. It is a bucket of twisted worms and your worm may have a twist of its own. If I had a full rack of bows and could not decide, I would buy the best chronograph that i could trust to help me decide.
However, I have an odd standard, the bow that I am most consistent with, taking varied shots at a fast tempo is always the bow that goes hunting. Fast or slow will make no difference in my decision.

Last edited by pavan; 07-30-2020 at 12:24 PM.
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  #5  
Old 07-30-2020, 08:18 AM
Tracker1 Tracker1 is offline
 
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Default Re: Poundage FPS

^^^^ Ok, my bow is a Samick Sage and my hunting limbs are 45lbs, my arrow is 550grn.
I’m thinking of going to 50lbs. Are you saying I could loose speed going to 50lbs, that sure goes against common thought.
I was trying to find what I might gain at 50 over the 45.
But I am thinking about another bow also. I really like the bow size and length but it seems to have a wall at 28” and at 29.5” that is not ideal for me.
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  #6  
Old 07-30-2020, 09:01 AM
Carboniac Carboniac is online now
 
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Default Re: Poundage FPS

You are not going to lose speed by getting heavier limbs for the same bow (unless theres something wrong with the limbs.)

But there are so many variables that its hard to predict what the increase willl be with a particular bow and arrow weight.
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  #7  
Old 07-30-2020, 09:36 AM
pipcount pipcount is offline
 
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Default Re: Poundage FPS

As others have stated, you never know. Even with limbs of same design, just heavier draw weight, results vary. You can make really rough guesstimates though.

A really rough idea, if you keep arrow mass constant, string constant, the draw force curves are REALLY similar just one is higher, etc. is that the the arrow speed should increase, roughly, as the square root of the increase in draw weight.

so here new speed ~old speed*sqrt(50/45). Sqrt(50/45) is ~1.05. So if you were at ~175FPS you should expect about the BEST you would see is about 5% more or 184FPS.

Is that likely- not really. Heavier draw limbs are heavier, draw curve likely a little different, generally less efficient, and you might have to increase your arrow spine, etc. etc. etc. But this gets you into a ballpark idea.

I think it is sort of interesting, but not REALLY interesting. More interesting is that as you increase draw weight ~11% your arrow will have less drop and is ~11% less. .This one breaks down as a simple rule that is good for small changes only. So you are less likely to miss due to range estimation errors.
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  #8  
Old 07-30-2020, 10:10 AM
rutandstrut rutandstrut is online now
 
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Default Re: Poundage FPS

Basically it should be roughly 2fps for every lb of draw weight. 5lbs draw weight will be not that noticeable in speed and penetration but it IS a big difference in holding weight. I would shoot the most weight you can shoot comfortably, accurately, and assuring first shot accuracy. Build an arrow around that. Good luck
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  #9  
Old 07-30-2020, 10:38 AM
Tracker1 Tracker1 is offline
 
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Default Re: Poundage FPS

Considering 45lbs seems to be the top end of my comfort zone and with all posts considered I’ll stick with 45lbs.
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  #10  
Old 07-30-2020, 10:40 AM
kentsabrina kentsabrina is offline
 
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Default

Let's say~~

I optimistically assume Sage will shoot 170fps with 8.5GPP

With 550gr arrow setup at 8.5GPP, u are looking at 64.7# actual draw weight


With that arrow setup n speed, u are achieving 35.29 foot pound of kinetic energy.
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  #11  
Old 07-30-2020, 10:50 AM
kentsabrina kentsabrina is offline
 
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But if u are only pulling 45# outta the sage

8.5GPP will be 382.5gr

170fps @ 382.5gr

U are looking at 24.5 foot pound of kinetic energy only

-------------

If u stick with 550gr with 45#

U are actually shooting 12GPP, the speed drops significantly, let's say 140fps

140fps @ 550gr

U are looking at 23.93 foot pound of kinetic energy

Last edited by kentsabrina; 07-30-2020 at 01:46 PM.
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  #12  
Old 07-30-2020, 12:46 PM
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Hank D Thoreau Hank D Thoreau is offline
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Default Re: Poundage FPS

I'll run that through my polynomial and linear draw force curve (DFC) models. It sounds like pipcount gave you the answer if you assume a linear DFC (constant spring constant). That model is okay in predicting trends, but you already know what the trend is....unless....

what Bowmania is referring to comes to pass. When Bowmania says that you may lose speed he is addressing the possibility that the bow may lose so much efficiency (probably through moving a heavier mass limb) that any gain in stored energy is cancelled out. I can't say that I have ever seen this but it is certainly possible. I have measured a very wide range of efficiencies, though I don't get the opportunity to test the same limb design in different weights.

https://tradtalk.com/forums/showthread.php?t=138241 Polynomial DFC
https://tradtalk.com/forums/showthread.php?t=135261 Linear DFC
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  #13  
Old 07-30-2020, 01:20 PM
kentsabrina kentsabrina is offline
 
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U need speed for kinetic energy

Higher the GPP, lower the speed
Lower the GPP, higher the speed

Given ur GPP is constant at your arrow choice, u can only adjust the # for speed

But not all limbs are created equal, let's say shooting the same 8.5 GPP:

Morrison Max 6 Medium 45#OTF
Samick Sage Medium 45# OTF

Morrison Max 6 Medium will be significantly faster, so given GPP is constant, but with higher speed, Morrison Max 6 Medium produces more kinetic energy than Samick Sage

Thats why u paid more money in equipment, u buy technology, performance, smoothness and easiness to achieve benchmark


But for all things, good or bad, there will always be an equilibrium

U can't expect gaining speed by upscaling the # regardlessly, and there is so much weight a person can handle healthly.


So chasing speed for producing highest kinetic energy possible for extremely heavy arrow only exists in calculation .

Everyone needs to find their sweet spot in choosing equipment.

In real world situation, a Morrison Max6 Short with 41# OTF shooting 15.8GPP heavy arrows (648gr arrow) can drop a 1200lbs eland antepone with authority. No FPS data on that kill record but I assume the FPS will be around 160fps.

So about 38.82 foot pound of kinetic energy is more than enough to kill most games.

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Last edited by kentsabrina; 07-30-2020 at 01:43 PM.
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  #14  
Old 07-30-2020, 02:09 PM
Tracker1 Tracker1 is offline
 
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Default Re: Poundage FPS

At 520grn at 45lbs I get 156fps.
At 445grn at 40lbs I get 158fps.
That is far from what I’m use to with my compounds but I have established a 20yard max for hunting with my recurves.
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  #15  
Old 07-30-2020, 02:34 PM
kentsabrina kentsabrina is offline
 
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520gr u are shooting 11.5GPP, kinetic energy is 28 foot pound.

445gr u are shooting 11.1GPP, kinetic energy is 24.6 foot pound.

If set a middle ground at 500gr in 45#, that is also 11.1GPP n should give u 157fps, 27.36 foot pound of kinetic energy.

So basically the same with heavier 520gr in 45#.......I will just go 520gr then, because the speed difference is neglectable and a heavier arrow makes a bow quieter.

May be swapping to a set of short sage limbs plus FF string can give u 165 fps max...Boosting the kinetic energy to 31 foot pound using 520gr arrow.

That should be ur sweet spot, according to my calculation...But I am no experienced hunter.
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