# Finally a flater shooting trajectory!!



## aquanator (Dec 1, 2005)

Recently I posted the thread asking how many sight pins you use. I was having difficulty getting one pin to work from 5 - 30 yards. My Matthews Legacy is set at 62 pounds because I like a fairly light draw, and I was shooting carbon express arrows weighing 12.6g per inch. I switched to lighter arrows which weigh 9.3g per inch, and the trajectory nicely flattened out so that my single pin now works from 5 to 30 yards!!!

I simply didn't realize that a 26% reduction in arrow weight would make such a big difference in arrow trajectory until I tried it! 

Over 30 years of bowhunting and I still feel like a "newbie" some days....


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## sbooy42 (Mar 6, 2007)

Just keep in mind you also lost 3.3gpi


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## aquanator (Dec 1, 2005)

Yep, I wish I knew the calc for kinetic energy so I could estimate the gain or loss (more speed but less weight, probably a lower kinetic energy I would guess?).

But I think 9.3g per inch is still a very "averge" arrow weight though, right? in the archery shop it appearred to be a pretty average weight for a carbon arrow.....


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## sbooy42 (Mar 6, 2007)

Oh yeah your still good to lay the smack down....


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## 454casull (Jan 6, 2005)

KE = Mass x Velocity x Velocity / 454240. You did lose some KE but the increased arrow speed made up a little of that. The flatter more forgiving traj. is worth it. You did not go nutz and drop below 6 GPI, that is when things have gone too far......


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## aquanator (Dec 1, 2005)

Excellent info 454, thanks!


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## aquanator (Dec 1, 2005)

454casull said:


> KE = Mass x Velocity x Velocity / 454240. You did lose some KE but the increased arrow speed made up a little of that. The flatter more forgiving traj. is worth it. You did not go nutz and drop below 6 GPI, that is when things have gone too far......


Hey, by my math using your calc, I actually gained some KE !!! Cool!!

Previous weight 465g, new weight 370g, previous speed 235 fps (est), new speed 270 fps (est), previous KE = 56.5, new KE = 59.3.

That assumes a 15% increase in speed after reducing total arrow weight by 20%. Which I think is close, since the new arrows are also thinner and drag less in my wicker biscket. 

I don't know how to actually measure arrow speed, but my Matthew's specs say my bow shoots from 235 (ammo) - 308 (IBO) fps, so I started on the low end. Not sure how accurate that is...

But, I'm especially looking forward to the first deer I take with it this fall!


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## Joe Archer (Mar 29, 2000)

aquanator said:


> Hey, by my math using your calc, I actually gained some KE !!! Cool!!


Sorry, this just doesn't happen. Lighter faster projectile will lose some KE. 
What Carbon Express were you using that weighed over 12 gr./inch?
<----<<<


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## aquanator (Dec 1, 2005)

I don't recall the exact name, and the archery shop guy told me that stopped making them, but they were something like "hunter's select"...nice camo arrows, I have 5 left that perhaps I'll use someday for something like shooting pigs.


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## 454casull (Jan 6, 2005)

Well after double checking the formula it does increase (57 v. 59), remember the speed is squared and if you pick up enough velocity it can give you more KE, his speeds are estimates mind you. His arrow is still near 400 grains and either 57-59 is plenty. My 370 gr arrow at 302 works out to 75# ke I love flat accurate arrows. Yep I am below 6 gpi. and that is by design; does not mean it is for everyone....


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## Atchison (Feb 18, 2009)

your arrow speed estimates are off which is why you think you have a higher KE, shoot through a chrono to verify either way the lower mass will help in the trajectory


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## aquanator (Dec 1, 2005)

Hmmm, unless you have some facts I don't, I don't see where my speed esitmates are off.....so, I gained a nice flat trajectory and kept or slightly increased my KE. I'm thrilled with that!!!!


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## misteelheader (Mar 4, 2006)

Its pretty simple math, the velocity is squared so a gain in velocity does a lot more for your kinetic energy than the weight of the arrow. I recently switched to the easton axis full metal jackets from maxima hunters. My maxima hunters were 100 grains less than my fmj's, after shooting it through the crono and calculating my kinetic energy it turned they both came out to be 80. Speed helps more for kinetic energy disproving the old myth that a youth hunter should shoot 125 grain broadheads over 85 grain broadheads.


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## jatc (Oct 24, 2008)

With a very efficient bow such as a Mathews solocam you often will end up with pretty much the same KE between a lighter/ faster arrow and a heavier/slower arrow. It is almost physically impossible however to actually GAIN KE by going to a lighter arrow. A bow is a machine that stores energy and then transmits the energy to the arrow. An efficient bow will transfer 80+% of its stored energy to the arrow. A heavier arrow will absorb (for lack of a better term ) more energy than a lighter arrow which tends to show up downrange where the heavier arrow will decelerate more slowly than the lighter arrow will. IE the lighter arrow will start out quicker , but it will lose speed at a quicker rate. In real world bowhunting the faster arrow is a better bet because even though it slows quicker, it will cover more ground in a shorter period of time giving gravity a shorter time in which to alter the course of the arrow. This is why with a lighter shaft you can use 1 pin out to 30 yards because it covers the distance quicker.

The energy not transferred to the arrow will go somewhere else when you release the string. This is why a heavy arrow will sound like a dull "thump" upon release whereas a lighter arrow will often have a slight "crack" to it. This is energy not absorbed by the arrow being released as vibration which in turn creates sound waves. This is the point of Harmonic Dampeners on a bow. They will arrest the vibration before they become sound waves.

This is why it is not good to shoot superlight arrows out of your bow. Anything less than 5 grains per pound of draw weight just can't absorb enough energy thereby giving the "dry fire" effect and destroying the bow in the process.


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## Chuck (Sep 24, 2000)

Here is a link to a online KE calculator

http://www.archeryhq.com/kin.htm


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## sullyxlh (Oct 28, 2004)

aquanator said:


> Hmmm, unless you have some facts I don't, I don't see where my speed esitmates are off.....so, I gained a nice flat trajectory and kept or slightly increased my KE. I'm thrilled with that!!!!


Shoot with a broadhead on and get back to us.........


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## sbooy42 (Mar 6, 2007)

sullyxlh said:


> Shoot with a broadhead on and get back to us.........


 
Yes please shoot your broadheads


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## Carlyle (Nov 19, 2007)

With out going into too much detail, here are my specs. All measured with good equipment, numerous times.

Carbon Matrix at 80-81 lbs depending on scale.
28.5 draw length
Both have Blazer X2's for fletch

Arrow 1 
*Flatline Surgical 340* 27.75 Shaft material 100 gr tip
363.4 grs
315.6 fps
80.39 lbs of KE
4.51grs/lb
12.59 FOC

Arrow 2 
*Easton** ACC Pro Hunter 300* 28.25 shaft material 125 gr tip
468.8 grs
281 fps
82.21 KE
5.68 grs/lb
13.51 FOC

I was hoping that my speed was going to be around 293fps with arrow 2, when using my archery software, but it just didn't happen. That would have put me at almost 90 KE. 105.4 grs more arrow only made 1.82 lbs of KE actual. Better luck next time. 

Not posting to get flamed for my setup just posting actual data. Yes I realize arrow 1 is light but its my bow.


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## FREEPOP (Apr 11, 2002)

jatc said:


> With a very efficient bow such as a Mathews solocam you often will end up with pretty much the same KE between a lighter/ faster arrow and a heavier/slower arrow. It is almost physically impossible however to actually GAIN KE by going to a lighter arrow. A bow is a machine that stores energy and then transmits the energy to the arrow. An efficient bow will transfer 80+% of its stored energy to the arrow. A heavier arrow will absorb (for lack of a better term ) more energy than a lighter arrow which tends to show up downrange where the heavier arrow will decelerate more slowly than the lighter arrow will. IE the lighter arrow will start out quicker , but it will lose speed at a quicker rate. In real world bowhunting the faster arrow is a better bet because even though it slows quicker, it will cover more ground in a shorter period of time giving gravity a shorter time in which to alter the course of the arrow. This is why with a lighter shaft you can use 1 pin out to 30 yards because it covers the distance quicker.
> 
> The energy not transferred to the arrow will go somewhere else when you release the string. This is why a heavy arrow will sound like a dull "thump" upon release whereas a lighter arrow will often have a slight "crack" to it. This is energy not absorbed by the arrow being released as vibration which in turn creates sound waves. This is the point of Harmonic Dampeners on a bow. They will arrest the vibration before they become sound waves.
> 
> This is why it is not good to shoot superlight arrows out of your bow. Anything less than 5 grains per pound of draw weight just can't absorb enough energy thereby giving the "dry fire" effect and destroying the bow in the process.


It is not physically impossible to increase KE. Look in Carlyl's post. Velocity is squared so it doesn't take much of a change to make a big difference.

The heavier arrow will also slow the bow down, resulting in a loss of speed for the arrow too. Which, as you stated, gives gravity more time to work on it and since it's heavier, compounds the rate of drop.

Friction is the major theif of energy.

The bow snaps back to it's original state when the arrow is released. A heavier arrow slows that process down, as resistance or load. Reduce that load to nothing or below a certail threshold and it can/will destroy itself.

Not disagreeing with you but stating differently.


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## jatc (Oct 24, 2008)

FREEPOP said:


> It is not physically impossible to increase KE. Look in Carlyl's post. Velocity is squared so it doesn't take much of a change to make a big difference.
> 
> The heavier arrow will also slow the bow down, resulting in a loss of speed for the arrow too. Which, as you stated, gives gravity more time to work on it and since it's heavier, compounds the rate of drop.
> 
> ...


The primary reason a light arrow will have less KE even though it is moving faster is the bow itself. A bow can only store X amount of energy at full draw regardless of the projectile used. A heavier arrow will except more energy than the lighter arrow will. This transmitted energy cannot exceed the energy stored in the bow. What I think this means is that with a 450 grain hunting arrow a bow might have an efficiency rating of 81% transferred energy, where with a 325 grain arrow it will probably transmit 79% energy. Therefore I hypothesize that there will be a 2% loss in kenetic energy with the lighter shaft. Definitely not enough to even care about.

Much of the confusion stems from guys estimating speed which works in theory but often will throw the numbers off just enough that the calculations will show a higher amount of KE for the lighter shaft. My experience (for what that means) bears out that estimated speeds that fall somewhere between AMO and IBO ratings of the bow most of the time are higher than actual. Even if your estimate is high by 5 fps, being that velocity is squared will often skew the results enough to show the faster shaft has a higher KE.

The only way to know for sure (and prove me wrong in the process) is to actually weigh and chronograph both arrows. A 12 pack says the heavier arrow will ALWAYS have a little more KE.


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## wolfgang510 (Feb 15, 2001)

Which Mathew's do you have? That is fast at 62 lbs to be able to shoot to 30 yds. I may have to upgrade my bow soon because I am not even comfortable 5-20. I have my first pin set at 17 yds.


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## triplelunger (Dec 21, 2009)

You guys need to find a physics forum!
I never thought deer hunting could be so nerdy!:lol:


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## aquanator (Dec 1, 2005)

wolfgang510 said:


> Which Mathew's do you have? That is fast at 62 lbs to be able to shoot to 30 yds. I may have to upgrade my bow soon because I am not even comfortable 5-20. I have my first pin set at 17 yds.


It's the Matthews Legacy. Quite an amazing bow when you review the specs from Matthews, even when shot next to the newer Drenalin's.


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## jc502 (Oct 8, 2002)

triplelunger said:


> You guys need to find a physics forum!
> I never thought deer hunting could be so nerdy!:lol:


We could go the quantum route and theorize that it has less KE, and more KE, at the same time.....


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## Hoyt_em (Aug 2, 2008)

wolfgang510 said:


> Which Mathew's do you have? That is fast at 62 lbs to be able to shoot to 30 yds. I may have to upgrade my bow soon because I am not even comfortable 5-20. I have my first pin set at 17 yds.


I'm guessing on his draw length at 29" and coming up with 270 fps, which equates out to 59# of KE...so I'm running a little bit high on my estimate. 

He isn't getting one pin to 30, there has to be some compensation either on the short side or the long side of where the pin is placed. 

My target set up is around 290 fps, and a 10 yard increase in distance with NO change to the pin, results in a drop of about 6" (ish).


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## Hoyt_em (Aug 2, 2008)

and before I get my *** handed to me...

here is the link/calc I used...
http://www.backcountrybowhunting.com/articles/tools.php


I used the information AQ gave us...308 IBO, 370 gn arrow, 29" draw (pure guess), 62# draw wieght, and 20 grains on the string (peep/Dloop)


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## willy05 (Nov 19, 2005)

I really do not care how much KE I have I punch a big hole through the deer and it dies.


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## aquanator (Dec 1, 2005)

Hoyt_em said:


> I'm guessing on his draw length at 29" and coming up with 270 fps, which equates out to 59# of KE...so I'm running a little bit high on my estimate.
> 
> He isn't getting one pin to 30, there has to be some compensation either on the short side or the long side of where the pin is placed.
> 
> My target set up is around 290 fps, and a 10 yard increase in distance with NO change to the pin, results in a drop of about 6" (ish).


 
Interesting to note everyone has different results. I used to have that 6"drop difference, point of this post is that I no longer have that, and the only thing that change is my arrows. I guess spped, KE, etc, are all "interesting" to some extent, but arrow flight and trajectory improvement was what I was after, and acheived!


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## FREEPOP (Apr 11, 2002)

You will probably more affected by wind drift now too.


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## Michigander84 (Apr 8, 2008)

Personally I'll take my heavier arrows at 270 fps and yes, I need a 20 and 30 yard pin but man-o-man do my Goldtips hit hard.


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## bishs (Aug 30, 2000)

Momentum is where it's at, when it comes to heavy arrows and penetration. Some may find this interesting.
My 57 lb recurve shot a 650 grain GoldTip 7595's, 160 fps,
I tuned using a bare shaft, and used a Silverflame, cut on contact two blade head. They are scary sharp...

I put that arrow compeletely through a broadside moose. It hanged out the opposite side then fell out as the moose ran 50 yards and fell.


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