Energy out of a bow

[PublicLandHunter1]

Is there a way to calculate how heavy an arrow needs to be to get the most energy out of your bow? I have a M405 and wonder how heavy I should go. Thanks in advance.

[xcaliber]

Well there might be some scientific responses, but I shoot a 355 Matrix, and 330 Matrix. I recently decided to test some Ape Tails just out of curiosity. My total weight is 528 grains, and I thought I was crazy giving up the speed I lost. I'll be honest here, I thought i would trash the whole idea. After several trips to the range with both bows, and leaving the chronograph home, I have decided to stay with these heavy arrows for this season. The bow is much quieter, and the penetration on the target is amazing. I hope to get a few kills this fall to make my mind up, but I would recommend that you stay over 400 grains. At that weight, these Excaliburs seem to perform real well, and the wind has less affect on the shot. My two cents!

[janesy]

Although I certain agree with the over 400 weight, I think with a 405 you can pretty much shoot any weight you want. It's going to hit hard.
Don't forget kinetic energy from a bow, IMHO, is a selling feature. Its asking a lot of an arrow to displace only enough energy to effectively pass through your game, and at that slow rate as well. The more energy it sheds, the less likely it is to pass through. And the sharper the Broadhead, the less energy it actually transfers to its game. Luckily enough, Excals have plenty of energy to shed.
Using rifle terminology to sell crossbows.

[gerald strine]

Buy some 2219 aluminum shafts and put a 150 grain slick trick on front and some blazer veins on the back and you will have a heavy arrow that will take advantage of that energy.
You should pass through everything in north america.
This is my set up on my Equinox and the bow loves it.
I squire both bolt ends and then the front and back incerts to eliminate fliers.
I be-leave you will want 22 inch shafts for that 405 as it has the same rail length as the Equinox, to get the bolt to extend into the stirup so you can not put your foot in to decock with a bolt on the rail and drive it through your foot. This set up will weigh about 525 grain range

[Ekkie]

Is there a way to calculate how heavy an arrow needs to be to get the most energy out of your bow? I have a M405 and wonder how heavy I should go. Thanks in advance.

The bow limbs store a specific amount of potential energy when cocked, and if you had a perfectly efficient setup then all that energy would be transferred to the arrow on the shot. There will always be some energy loss though (vibrations of the crossbow, noise, string stretch, heat, etc), so the arrow will always have less than the theoretical max kinetic energy that it could have. The heavier the arrow, the more kinetic energy it will have when shot, but there obviously comes a point where it just doesn't matter anymore.

I do favor heavier arrows. I hunt with 535 grain arrows (18.5" FMJs with brass inserts and 125 grain Slick Tricks). Heavier arrows are easier on the bows, quieter on the shot, retain their KE further down field, are less affected by the wind, and are less likely to be deflected if it encounters a leaf or small twig in flight. Personally I'd never go below 450 grains for a M405, but that's just my opinion. In a couple weeks I'll be hunting with those 535 grain FMJs out of a Matrix 380.

Best of luck,
~E

[Timbrhuntr]

Is there a way to calculate how heavy an arrow needs to be to get the most energy out of your bow? I have a M405 and wonder how heavy I should go. Thanks in advance.

http://archerycalculator.com/archery-kinetic-energy-and-momentum-calculator/

[xcaliber]

Yep, a scooter doing 50 hits a brick wall, some blood and scratches on the bricks, a bus hits the wall going 35, bricks get knocked out!

[Ekkie]

...
If you keep adding arrow weight at a certain point you will lose enough speed that KE will actually will go down but momentum will keep going up.
...

I see no reason why this should be true; KE should always increase with a heavier arrow as long as the bow itself doesn't absorb more of the potential energy from the limbs (like say for example due to recoil). Have you actually measured a decrease in KE with rising arrow weights?

A bow / arrow can easily be viewed as a conservation of energy problem. There is a set amount of potential energy in the cocked crossbow limbs, which would correspond to the absolute theoretical limit of the KE of the arrow at the shot. After the shot the limbs contain no more potential energy. If the arrow didn't absorb it, then it had to go somewhere else... like into recoil, or vibrations / heat.

~E

[longbow joe]

I used to shoot 16.5 inch 2219 alluminums out of my micro with the now (stupidly ) discontinued slick trick 175 grain crossbow .l shot a 225 lb full size 9 pointer coming at me with one. The bolt went all the way thru the buck lengthwise and never found it. The 175 was also perfect foc for a heavy shaft like that .....good stuff.

[nchunterkw]

I used to shoot 16.5 inch 2219 alluminums out of my micro with the now (stupidly ) discontinued slick trick 175 grain crossbow .l shot a 225 lb full size 9 pointer coming at me with one. The bolt went all the way thru the buck lengthwise and never found it. The 175 was also perfect foc for a heavy shaft like that .....good stuff.

Joe
Putting these numbers in the calculator above for a 405 bow, assuming 3fpsloss per grain above 350gr arrow

500 gr arrow. 500-350 = 150gr/3 - 50fps loss, so speed is 355fps
KE = 139.77, Mom. = 0.787

600 gr arrow. 600-350 = 250gr/3 - 83fps loss, so speed is 322fps
KE = 138, Mom. = 0.857

Since:
P = mV (P is momentum)
and
KE = 1/2 mV^2 the KE will drop exponentially by the square of the velocity as velocity decreases.

Keep in mind that Ed Ashby suggests and arrow with a P of 0.6 or greater for excellent penetration. IMO a 500 gr arrow from a 405 bow would be more than adequate on just about any animal, let alone anything in North America.

FWIW
Heavy arrow options that work in my Micro at 16" are:
GoldTip Nitro Pro (14 GPI), and
Easton FMJ (14.1GPI)

I give the edge to the GT as it is all carbon. The FMJ is Al over carbon and can bend. Also, I worked with NuFletch and they now offer Igniters for the GT arrow (ID is about 0.275ish", if I remember right )

[hunter with MS]

The formula for figuring ke energy from a bow is arrow speed times arrow speed times total arrow weight with broadhead or field point divided by 450 240 that will give you the energy out of the bow including a crossbow so my crossbow speed say is 330 X 330 x 375 divided by 450240 = 90 pounds of KE energy

[Ekkie]

...
FWIW
Heavy arrow options that work in my Micro at 16" are:
GoldTip Nitro Pro (14 GPI), and
Easton FMJ (14.1GPI)
...

Can I ask what FMJ shaft you're shooting? The ones I'm shooting (with the standard crossbow shaft OD of ~22/64") are 13.7 GPI according to Easton. Their specs might be wrong though... wouldn't be the first time. I haven't actually measured the shaft weight so I don't know for sure.

Thanks,
~E

[nchunterkw]

Can I ask what FMJ shaft you're shooting? The ones I'm shooting (with the standard crossbow shaft OD of ~22/64") are 13.7 GPI according to Easton. Their specs might be wrong though... wouldn't be the first time. I haven't actually measured the shaft weight so I don't know for sure.

Thanks,
~E

I bought a bunch of FMJ shafts like 6 yrs ago and I thought that was the number. I could be wrong as well, but they were definitely heavier than 13.7GPI. It was 14 or 14.1 Perhaps they have changed them since then, but I too was going off of their specs. But it all seemed to work out as my 20" arrows weight in the 525gr neighborhood as I recall. Had brass inserts...

I have records somewhere at home I can look up tonight.

[SEW]

Concerning energy retained verses trajectory, there are tradeoffs. For me, I want enough energy to to get a passthru on the game I hunt. My largest game are bear and deer. Traditionally, 30-40'-lbs has been considered adequate; however, with so much energy often available over this, larger broadheads have been developed which require more energy. Some may actually require 50-70 ft-lbs for a clean passthru.

I did a test last February to see what the actual energy loss is out to 100 yards. Reason - I kept reading posts about not shooting beyond certain ranges because "not enough energy " would remain. I didn't believe that there was really that much bleed-off of energy with modern, low drag , xbow arrows. I think much of traditional "energy/velocity" loss thought comes from traditional, traditional arrows (the double traditional isn't accidental - my traditional arrows are more modern). 5" helical feathers are like sea anchors.

Which is more important, energy or trajectory? For me, after obtaining adequate energy, I want the flattest trajectory possible. I don't understand any desire for energy beyond the max needed at the sacrifice of trajectory. Who doesn't want a flatter trajectory?

Below are my test results:


20" ST 418.6g M405
1yd 369'/sec 127ft-lbs.
20yd 360'/sec 120.
40yd 354'/sec 117.
60yd 337'/sec 106.
80yd 325'/sec 98.
100yd 311'/sec 90.
So from 20 yards to 100 yards only 58'/sec (16%) was lost while only 30ft-lbs (25% )of the energy was lost. More energy was lost due to the speed squared factor of the formula E= MC(2). Any energy above the minimum required (34'-pds) or desired (40'-lbs) for deer (20 more for bear), is just gravy. These energy levels are for "average" fixed blade broadheads. I believe I read a post by Boo stating that once desired energy has been reached, trying to get more energy by sacrificing speed is not desirable. I agree totally. With this in mind, the energy loss of 25% from 20-100 yards is irrelevant since still over twice the energy still remains than is needed.

So, what can we derive from this? First off, my heavily noise/vibration attenuated M405 is just upper mid level performance wise. These shots were all made with a 5-8 mph l-r xwind. The accuracy of the M405/20", 92g insert, 125 Griz Trick, helical Blazers, flat plastic nocks is incredible. Since the M405 is actually sighted in with Lumenoks , I aimed off slightly to help preserve my chronograph . Still I felt comfortable testing out this far. No target practice has been done with this Xbow since mid-September. Its only shots were deer kills. It's still on, even with nearly 20g of difference in the nocks.
Back to the results. Contrary to what many have stated, energy loss seems to be a non-factor even out to 100 yards. Trajectory, range estimation error, and time of flight remain the critical and limiting factors. O.88 sec to 100 yds, 0.51 sec to 60 yds.

Why all this? Because of repeated comments on various forums concerning loss of energy at what many consider "extended" ranges (40-60 yards). I've been repeatedly chastised for shooting at these ranges because "not enough energy" remains for an ethical kill. False!! However, some broadheads can require a tremendous amount of energy to get a passthru (FOCs). After all my promotion of FOCs for higher powered xbows, I've now discontinued their usage in favor of (currently -verdict not in) Grizz Tricks. I want passthru's . I killed a 100#+ doe p(though the picture doesn't look like it's that large) last Fri with a GT(2nd deer of year with this BH). Massive blood trails.

[SEW]

Concerning energy retained verses trajectory, there are tradeoffs. For me, I want enough energy to to get a passthru on the game I hunt. My largest game are bear and deer. Traditionally, 30-40'-lbs has been considered adequate; however, with so much energy often available over this, larger broadheads have been developed which require more energy. Some may actually require 50-70 ft-lbs for a clean passthru.

I did a test last February to see what the actual energy loss is out to 100 yards. Reason - I kept reading posts about not shooting beyond certain ranges because "not enough energy " would remain. I didn't believe that there was really that much bleed-off of energy with modern, low drag , xbow arrows. I think much of traditional "energy/velocity" loss thought comes from traditional, traditional arrows (the double traditional isn't accidental - my traditional arrows are more modern). 5" helical feathers are like sea anchors.

Which is more important, energy or trajectory? For me, after obtaining adequate energy, I want the flattest trajectory possible. I don't understand any desire for energy beyond the max needed at the sacrifice of trajectory. Who doesn't want a flatter trajectory?

Below are my test results:


20" ST 418.6g M405
1yd 369'/sec 127ft-lbs.
20yd 360'/sec 120.
40yd 354'/sec 117.
60yd 337'/sec 106.
80yd 325'/sec 98.
100yd 311'/sec 90.
So from 20 yards to 100 yards only 58'/sec (16%) was lost while only 30ft-lbs (25% )of the energy was lost. More energy was lost due to the speed squared factor of the formula E= MC(2). Any energy above the minimum required (34'-pds) or desired (40'-lbs) for deer (20 more for bear), is just gravy. These energy levels are for "average" fixed blade broadheads. I believe I read a post by Boo stating that once desired energy has been reached, trying to get more energy by sacrificing speed is not desirable. I agree totally. With this in mind, the energy loss of 25% from 20-100 yards is irrelevant since still over twice the energy still remains than is needed.

So, what can we derive from this? First off, my heavily noise/vibration attenuated M405 is just upper mid level performance wise. These shots were all made with a 5-8 mph l-r xwind. The accuracy of the M405/20", 92g insert, 125 Griz Trick, helical Blazers, flat plastic nocks is incredible. Since the M405 is actually sighted in with Lumenoks , I aimed off slightly to help preserve my chronograph . Still I felt comfortable testing out this far. No target practice has been done with this Xbow since mid-September. Its only shots were deer kills. It's still on, even with nearly 20g of difference in the nocks.
Back to the results. Contrary to what many have stated, energy loss seems to be a non-factor even out to 100 yards. Trajectory, range estimation error, and time of flight remain the critical and limiting factors. O.88 sec to 100 yds, 0.51 sec to 60 yds.

Why all this? Because of repeated comments on various forums concerning loss of energy at what many consider "extended" ranges (40-60 yards). I've been repeatedly chastised for shooting at these ranges because "not enough energy" remains for an ethical kill. False!! However, some broadheads can require a tremendous amount of energy to get a passthru (FOCs). After all my promotion of FOCs for higher powered xbows, I've now discontinued their usage in favor of (currently -verdict not in) Grizz Tricks. I want passthru's . I killed a 100#+ doe p(though the picture doesn't look like it's that large) last Fri with a GT(2nd deer of year with this BH). Massive blood trails.