Getting my Bow to shoot faster without losing KE?
07-22-2009, 12:42 AM
#11
Spike
Join Date: Jul 2009
Location: Barbour Co. West Virginia
Posts: 90
Berettaguy....There is no way that 224 is a KE reading. I think that is an IBO speed calculation.
Anyway I ran some numbers. Are you ready for this.....
Your Current Setup: 475gr arrow @ 221fps = 51.53 ft/lbs of KE
If you lighten your arrow: 325gr arrow @ 285fps = 58.63 ft/lbs of KE
As predicted the faster arrow speed increased your KE. That is something that you have to show most guys, especially us old school guys. But it made sense to me as soon as I learned the formula....when the arrow speed is squared (speed x speed) it has to make a bigger difference than the arrow weight. The formula for KE is as follows: KE= Velocity Squared (arrow speed x arrow speed) X Mass (arrow wt) \ Divided By 450,240.
Anyway here is a link. http://www.archeryhq.com/kin.htm
So, like I said in our PM. Get those new Radial X weaves you were wanting and get them cut down. I knew your arrows had to be waaay too long to weigh that much. I been around the block a few times.
Just glad I could help.
Holler Back ....If ya need me.
Dryridge
Anyway I ran some numbers. Are you ready for this.....
Your Current Setup: 475gr arrow @ 221fps = 51.53 ft/lbs of KE
If you lighten your arrow: 325gr arrow @ 285fps = 58.63 ft/lbs of KE
As predicted the faster arrow speed increased your KE. That is something that you have to show most guys, especially us old school guys. But it made sense to me as soon as I learned the formula....when the arrow speed is squared (speed x speed) it has to make a bigger difference than the arrow weight. The formula for KE is as follows: KE= Velocity Squared (arrow speed x arrow speed) X Mass (arrow wt) \ Divided By 450,240.
Anyway here is a link. http://www.archeryhq.com/kin.htm
So, like I said in our PM. Get those new Radial X weaves you were wanting and get them cut down. I knew your arrows had to be waaay too long to weigh that much. I been around the block a few times.
Just glad I could help.
Holler Back ....If ya need me.
Dryridge
Last edited by dryridge2; 07-22-2009 at 01:03 AM.
07-22-2009, 06:01 PM
#12
Nontypical Buck
Join Date: Dec 2005
Location: Burke, VA (raised in MD)
Posts: 1,096
07-22-2009, 06:54 PM
#13
Boone & Crockett
Join Date: Feb 2003
Posts: 10,679
Dryridge, where did you pull 285 fps from?
There is no way he will get 285 fps out of that bow with a 325 grain arrow. He will be lucky to break 270fps.
Start with an IBO of 316fps.
Subtract 40fps for his draw length.
Subtract 6 fps for his peep sight and you are at 270fps.
His KE would likely decrease by about one foot pound or more by going to that lighter weight arrow.
As the arrow gets lighter the the bows efficiency decreases and the speed per grain of arrow weight decreases.
There is no way he will get 285 fps out of that bow with a 325 grain arrow. He will be lucky to break 270fps.
Start with an IBO of 316fps.
Subtract 40fps for his draw length.
Subtract 6 fps for his peep sight and you are at 270fps.
His KE would likely decrease by about one foot pound or more by going to that lighter weight arrow.
As the arrow gets lighter the the bows efficiency decreases and the speed per grain of arrow weight decreases.
Last edited by bigbulls; 07-22-2009 at 06:56 PM.
07-22-2009, 09:56 PM
#14
Nontypical Buck
Join Date: Mar 2008
Location: Henderson, KY
Posts: 1,760
http://www.backcountrybowhunting.com/articles/tools.php
That is the calculator is use. Ive found it to be VERY accurate so long as the bow will shoot its ibo speed... Most newer bows dont really have that problem...
Dryridge, not only will he not gain that much speed, or gain that much ke, he will also loose momentum! Much more important than speed or ke when talking about lower weight/slower setups...
He would be way better off in reality using the arrow he is now.
Derek
That is the calculator is use. Ive found it to be VERY accurate so long as the bow will shoot its ibo speed... Most newer bows dont really have that problem...
Dryridge, not only will he not gain that much speed, or gain that much ke, he will also loose momentum! Much more important than speed or ke when talking about lower weight/slower setups...
He would be way better off in reality using the arrow he is now.
Derek
07-23-2009, 03:41 AM
#15
Giant Nontypical
Join Date: Feb 2003
Location: the woods of NJ.
Posts: 5,643
07-23-2009, 05:49 AM
#16
Nontypical Buck
Join Date: Feb 2007
Location: SE Ohio
Posts: 2,531
Not that great of an improvement, and if he don't have good strings, he's gonna deal with peep rotation. I'd say KEEP the peep, and look at the rest of the set-up.
Agreed.....
While I agree the numbers may be a touch off, the rest of the post is MONEY!!!
With your set-up, you should be shooting a .450 spine arrow, and most arrow in a .450-ish spine will be under 400 gr's all set-up, several are in the 375-385gr range, and that is with a 125gr tip to balance out the spine, while also gets your FOC up.
......But if you are just learning the mechanics of archery it gets pretty technical sometimes and we all forget we didn't start out with 20yrs experience fooling with these things....(33 in my case). With that said, here's what you can do and why.
You can drop your arrow weight significantly. I can't imagine what kind of arrows you are shooting that are not really overspined at that weight anyway... unless they are extremely long. Your bow is obviously tuned decent if you can shoot well with those arrows. The drop away rest is helping.
Agreed wholeheartedly....
By the way what arrow/length/tip wt are you shooting? Also what type of broadhead.
( I should have asked that first, but I don't think it is going to matter a lot)
Remember do not go below 5gr total arrow setup wt for every pound of peak draw wt. which in your case is 325gr total arrow wt. Remember to add for fletching, glue and nock. roughly 25gr total w/Blazers, more w/longer fletch. If you didn't actually weigh your arrow or add that in, you may be closer to 500gr.
Bottomline...... Cutting that 150gr off your arrow could potentially bring your arrow speed up by 75 fps.....But I would guess more like 60 or so. Remember, there is a point of diminishing return. And I bet you a nickel that you will be able to get rid of one of your pins out to 30yds.
Go play on the KE Calculator and see what happens. Put in 325gr arrow and 285fps. Then try some numbers in between.
Also as far as arrows yo should be able to get that length down to 25 3/4" if you want. That makes them faster and something you prob. never thought of....easier to carry in the woods/brush. Also it has been proven that a shorter arrow flies better with a FOC of 10% or more. If you aren't familiar that means it should balance about 2 3/4" or further forward of the center point of the arrow with the broadhead installed.
I know you asked for the time I built you a watch...but if you are like me, I gotta know why it works before I do it. And if I know why, I will more likely have confidence that it will work.
Good Luck Buddy, Holler at me if you run into snags or if you find I am way off base.
Dryridge
Dryridge
You can drop your arrow weight significantly. I can't imagine what kind of arrows you are shooting that are not really overspined at that weight anyway... unless they are extremely long. Your bow is obviously tuned decent if you can shoot well with those arrows. The drop away rest is helping.
Agreed wholeheartedly....
By the way what arrow/length/tip wt are you shooting? Also what type of broadhead.
( I should have asked that first, but I don't think it is going to matter a lot)
Remember do not go below 5gr total arrow setup wt for every pound of peak draw wt. which in your case is 325gr total arrow wt. Remember to add for fletching, glue and nock. roughly 25gr total w/Blazers, more w/longer fletch. If you didn't actually weigh your arrow or add that in, you may be closer to 500gr.
Bottomline...... Cutting that 150gr off your arrow could potentially bring your arrow speed up by 75 fps.....But I would guess more like 60 or so. Remember, there is a point of diminishing return. And I bet you a nickel that you will be able to get rid of one of your pins out to 30yds.
Go play on the KE Calculator and see what happens. Put in 325gr arrow and 285fps. Then try some numbers in between.
Also as far as arrows yo should be able to get that length down to 25 3/4" if you want. That makes them faster and something you prob. never thought of....easier to carry in the woods/brush. Also it has been proven that a shorter arrow flies better with a FOC of 10% or more. If you aren't familiar that means it should balance about 2 3/4" or further forward of the center point of the arrow with the broadhead installed.
I know you asked for the time I built you a watch...but if you are like me, I gotta know why it works before I do it. And if I know why, I will more likely have confidence that it will work.
Good Luck Buddy, Holler at me if you run into snags or if you find I am way off base.
Dryridge
Dryridge
Dryridge, where did you pull 285 fps from?
There is no way he will get 285 fps out of that bow with a 325 grain arrow. He will be lucky to break 270fps.
Start with an IBO of 316fps.
Subtract 40fps for his draw length.
Subtract 6 fps for his peep sight and you are at 270fps.
His KE would likely decrease by about one foot pound or more by going to that lighter weight arrow.
As the arrow gets lighter the the bows efficiency decreases and the speed per grain of arrow weight decreases.
There is no way he will get 285 fps out of that bow with a 325 grain arrow. He will be lucky to break 270fps.
Start with an IBO of 316fps.
Subtract 40fps for his draw length.
Subtract 6 fps for his peep sight and you are at 270fps.
His KE would likely decrease by about one foot pound or more by going to that lighter weight arrow.
As the arrow gets lighter the the bows efficiency decreases and the speed per grain of arrow weight decreases.
With your set-up, you should be shooting a .450 spine arrow, and most arrow in a .450-ish spine will be under 400 gr's all set-up, several are in the 375-385gr range, and that is with a 125gr tip to balance out the spine, while also gets your FOC up.
07-23-2009, 04:25 PM
#17
Spike
Join Date: Jul 2009
Location: Barbour Co. West Virginia
Posts: 90
In the KE equation....the speed is squared. That means speed has a greater effect on KE than the weight. Which means you can shed weight, add speed and actually increase your KE slightly in your case. However, there is a point of diminishing return on that as well. I would do it for the gain in trajectory. I never cared so much about how fast my arrow was going, but I did care about how flat it shot. How many misses are left and right? Not many. You either miss high or low. Putting that arrow on a diet will take some of the arch out of your archery and that will give you the speed and KE retention you want and the improved trajectory you need.
Go to an oline KE calculator and play around with the weights and speed and you will see what I mean. However you have to remember to come up with a way to get a speed increase to add as well. You can do that for your bow by adding about 1 fps for every 2grains of arrow weight you decrease . Your bow now shoots 221fps with a 475gr arrow, or about 1fps for every 2grs of arrow wt.
Go to an oline KE calculator and play around with the weights and speed and you will see what I mean. However you have to remember to come up with a way to get a speed increase to add as well. You can do that for your bow by adding about 1 fps for every 2grains of arrow weight you decrease . Your bow now shoots 221fps with a 475gr arrow, or about 1fps for every 2grs of arrow wt.
BIG BULLS>>>> Thanks For Asking.....I got it from the statement above....last paragraph, I know it's too long. I would bet, with that bow and that set up, he will get that...Unless he does not have the correct cam for that draw length and that isn't likely.
It is science. While I agree there is a point of diminishing return, simple math is easy enough. At least I used known quotients for the equation. I guess I could do likewise and ask where you pulled the fps reductions you used from, but I'm not like that. Matter of fact I tend to agree you were close, but you used fudge factor numbers that are thrown out to "all comers". His bow happens to be a harsh cam and known for spitting out speed. I'll stick with my equation.
DROCKW....You Say: Dryridge, not only will he not gain that much speed, or gain that much ke, he will also loose momentum! Much more important than speed or ke when talking about lower weight/slower setups...
I happen to think it will gain that much and I said why above. So, maybe you disagree and that's fine. That's what makes us free people. I appreciate that.
I also said the exact same thing you did about the importance of MOMENTUM instead of KE in my first post.
And while I will admit that I cheated and used an online calculator and did not do the longhand math.....Increasing Speed DOES increase KE that much. Again, speed is squared, therefore it has a much greater effect on the equation than mass. Do the math and see. But my friend, this argument is really not worth having. They are totally different measurement of enegy, one is based on velocity the other mass. While momentum decreases at about the same rate KE increases, does that mean that KE energy is useless?Momentum doesn't flatten trajectory, it hurts it...and I would rather be able to hit something with a faster,flatter, lighter arrow, and let Good, Sharp, broadhead....the only killing part of the whole set up.... do it's work, than miss with a pile-driver. But that's only based or nearly 40yrs of hunting, factory staff shooting and pro shop owning and more importantly over 300 dead animals.
Slow set ups don't gain HUGE amounts of momentum no matter what you do. At least not enough to make a real apprecialble difference in raw, penetrating power. Can we agree on that? SO, my hypothesis is that we should make it more effective where we can and take some of the arch out, give it a little more umph and make a good hit. My last 2 archery deer were shot with a custom 32# bow built by a top manufacturer for me follow my shoulder reconstruction (too many years of too many bows) and light weight (5.3gr/lb) carbons tipped with Magnus Stingers. Complete passthroughs and both dropped in sight.
While we can argue the differences in energy measurements, there is one stage of dead and it speaks for itself.
If I am wrong I apologize fellows....but I don't think I'm that far off.
Respectfully,
Dryridge
Last edited by dryridge2; 07-24-2009 at 08:16 AM. Reason: I wrote "They are totally different measurement of enegy, one is based on velocity the other Momentum...it should read MASS.
07-23-2009, 06:15 PM
#19
Boone & Crockett
Join Date: Feb 2003
Posts: 10,679
You can certainly take the "arch" out by using a lighter weight arrow but I have never seen a bow that will gain KE by shooting a lighter arrow.
Well, I say never. I have seen a few bows that have gained a foot pound over a slightly heavier arrow every now and then. I can only assume that some bows have a "sweet spot" as far as their efficiency goes in relation to arrow weight.
I am not trying to be argumentative but if he expects to get 285 with an IBO weighted arrow he is going to be disappointed.
Since I don't have his bow here to shoot through a chrono lets use my bow for example.
Bowtech Captain, 70 pound draw weight, 30" draw length, 437 grain arrow, 293 fps for 83 foot pounds of KE. I have two tied in nocks between a loop and a peep sight with no rubber tubing. If I calcualted how you describe I should be able to get about 337 fps and 88 foot pounds of KE out of my bow with a 350 grain arrow like it sits right now. I have not chronographed it with a 350 grain arrow yet but I bet it will only get about 320 to 323 and my KE number is going to be about 80 foot pounds.
Now, Having said all of this he can certainly pick up quite a bit of speed if he is willing to spend some money. Since he is shooting 65 pounds with only a 26" DL he could stand to loose a couple of strands in his string. He could have a thinner and lighter string made with thinner and stronger string material than 8125 that PSE uses and still be plenty strong and safe. Then he could shorten his center serving to only about 3 inches long, loose the big peep with rubber tube and get a G5 meta peep.
Well, I say never. I have seen a few bows that have gained a foot pound over a slightly heavier arrow every now and then. I can only assume that some bows have a "sweet spot" as far as their efficiency goes in relation to arrow weight.
I am not trying to be argumentative but if he expects to get 285 with an IBO weighted arrow he is going to be disappointed.
Since I don't have his bow here to shoot through a chrono lets use my bow for example.
Bowtech Captain, 70 pound draw weight, 30" draw length, 437 grain arrow, 293 fps for 83 foot pounds of KE. I have two tied in nocks between a loop and a peep sight with no rubber tubing. If I calcualted how you describe I should be able to get about 337 fps and 88 foot pounds of KE out of my bow with a 350 grain arrow like it sits right now. I have not chronographed it with a 350 grain arrow yet but I bet it will only get about 320 to 323 and my KE number is going to be about 80 foot pounds.
Now, Having said all of this he can certainly pick up quite a bit of speed if he is willing to spend some money. Since he is shooting 65 pounds with only a 26" DL he could stand to loose a couple of strands in his string. He could have a thinner and lighter string made with thinner and stronger string material than 8125 that PSE uses and still be plenty strong and safe. Then he could shorten his center serving to only about 3 inches long, loose the big peep with rubber tube and get a G5 meta peep.
07-23-2009, 10:27 PM
#20
Spike
Join Date: Jul 2009
Location: Barbour Co. West Virginia
Posts: 90
Big Bulls
The last thing I want to do is argue, and I am not above making mistakes or getting things mixed up. The one thing I always do is learn from my mistakes. That said, I went back and did all the numbers on my own without the cheater. My FPS were indeed off. I was just estimating. It was 279.14fps. That brings the KE down to 56.24
When I did your numbers I got exactly what you did by rounding off. So, knowing the differerence was in efficiency I realized that your bow had nearly reached that point of diminishing return that bites you in the butt when using KE as the measurement of choice (it's why crossbows aren't as fast or have the penetration of a good compound set up unless you get up into crazy poundages over 200#) So, I used an old formula I developed in the 80's when "Cams" replaced "wheels" to see just how much they improved things and where the "Point of Negative Return" was. It's more a measurement of potential or stored energy, vs expressed or expended energy. Does that make sense BBs? Just like opinions and arguments it's all mine and I don't expect anyone else to buy into it, but to me it makes sense....Anyway, I got efficiency ratings of 1.491 for your setup and 2.15 for his. You see his draw length (power stroke) and way too heavy arrow (excessive mass) have his bow choked and therefore still storing way more energy per pound than it is expending. Thus, by decreasing the mass we release more energy in his set up than yours, which is already nearing peak performance. This will hold true in it's velocity and therefore the KE.
What would be interesting is if both of you could shoot the light arrows through a crony and see what happens. But I'd say you are right all around on what your bow will do based on it's being at near peak efficiency, it will gain less, and yes even lose. You know when cams hit the market their intention was to send the same wt. arrow at a higher velocity. This does improve any measurement of energy you want to use. Then guys like me started coming up with ways to make them lighter, faster. Oh well, thats another story for another day. But lets say my "Speed Record" if the early technology chrono sitting outside on a sunny day was accurate.... printed a 10shot avg of 411 in 1988 I think it was.... I can't recall for certain. The bow a handbuilt 108#PSE Mach 4 with an overdraw I machined for it. I was shooting 24" Easton xx75 2020 shafts with a draw length of 31.5". There were no targets to stop it without driving the inserts into the shafts. Finally compressed soaked wood shaving bales with mine belt hanging loosely behind worked. I had arrows explode in mid air. It was a beast of burden and I am very lucky to not have gotten injured. It nearly ruined my bowhunting. It was a rifle. I hunted by sneaking along field edges and took deer at....way too far to say. I dismantled it, put 70# limbs on it and sold it on the used rack in my shop. Funny, now that my health is gone, I am forced to use a crossbow for hunting. I have one with a 225# draw and it doesn't shoot near as fast as that old PSE....The efficiency is maxed out. You know I used my equation on it....it's like 0.46 I think...Grossly inefficient.
Anyway BigBulls....You know your stuff, as evidenced by knowing the "fudge factors for all the different areas of influence and the string discussion...no doubt about it. But go a tad deeper when looking at influences as one bow will be more receptive to some tweaks than others. I have spent 30yrs trying to figure out which and why. I'm through, you're still in the game, If you get it nailed down, let me know, wouldja!!! It's another dimension....Just like 3rd axis and now 4th axis sighting/aiming!!! Who'da Thunk It!!!!
RESPECT!
Dryridge
The last thing I want to do is argue, and I am not above making mistakes or getting things mixed up. The one thing I always do is learn from my mistakes. That said, I went back and did all the numbers on my own without the cheater. My FPS were indeed off. I was just estimating. It was 279.14fps. That brings the KE down to 56.24
When I did your numbers I got exactly what you did by rounding off. So, knowing the differerence was in efficiency I realized that your bow had nearly reached that point of diminishing return that bites you in the butt when using KE as the measurement of choice (it's why crossbows aren't as fast or have the penetration of a good compound set up unless you get up into crazy poundages over 200#) So, I used an old formula I developed in the 80's when "Cams" replaced "wheels" to see just how much they improved things and where the "Point of Negative Return" was. It's more a measurement of potential or stored energy, vs expressed or expended energy. Does that make sense BBs? Just like opinions and arguments it's all mine and I don't expect anyone else to buy into it, but to me it makes sense....Anyway, I got efficiency ratings of 1.491 for your setup and 2.15 for his. You see his draw length (power stroke) and way too heavy arrow (excessive mass) have his bow choked and therefore still storing way more energy per pound than it is expending. Thus, by decreasing the mass we release more energy in his set up than yours, which is already nearing peak performance. This will hold true in it's velocity and therefore the KE.
What would be interesting is if both of you could shoot the light arrows through a crony and see what happens. But I'd say you are right all around on what your bow will do based on it's being at near peak efficiency, it will gain less, and yes even lose. You know when cams hit the market their intention was to send the same wt. arrow at a higher velocity. This does improve any measurement of energy you want to use. Then guys like me started coming up with ways to make them lighter, faster. Oh well, thats another story for another day. But lets say my "Speed Record" if the early technology chrono sitting outside on a sunny day was accurate.... printed a 10shot avg of 411 in 1988 I think it was.... I can't recall for certain. The bow a handbuilt 108#PSE Mach 4 with an overdraw I machined for it. I was shooting 24" Easton xx75 2020 shafts with a draw length of 31.5". There were no targets to stop it without driving the inserts into the shafts. Finally compressed soaked wood shaving bales with mine belt hanging loosely behind worked. I had arrows explode in mid air. It was a beast of burden and I am very lucky to not have gotten injured. It nearly ruined my bowhunting. It was a rifle. I hunted by sneaking along field edges and took deer at....way too far to say. I dismantled it, put 70# limbs on it and sold it on the used rack in my shop. Funny, now that my health is gone, I am forced to use a crossbow for hunting. I have one with a 225# draw and it doesn't shoot near as fast as that old PSE....The efficiency is maxed out. You know I used my equation on it....it's like 0.46 I think...Grossly inefficient.
Anyway BigBulls....You know your stuff, as evidenced by knowing the "fudge factors for all the different areas of influence and the string discussion...no doubt about it. But go a tad deeper when looking at influences as one bow will be more receptive to some tweaks than others. I have spent 30yrs trying to figure out which and why. I'm through, you're still in the game, If you get it nailed down, let me know, wouldja!!! It's another dimension....Just like 3rd axis and now 4th axis sighting/aiming!!! Who'da Thunk It!!!!
RESPECT!
Dryridge
Last edited by dryridge2; 07-23-2009 at 11:19 PM.