Arrow energy question!

[bowhunterportugal]

Hi gang,

It's been a wile since I've post here. Work and hunt and hunt and work...

Here's a question.

A friend of mine bought some Axis FMJ Dangerous Game spine 300. Those are heavy and strong arrows, very beautiful, fly great, amazing penetration so they must be good, no doubt. With 75 grain HIT insert and a 125 grain tip they pass the 700 grain mark.

I shoot CE Heritage 250, total weight of 623 grains and a softer spine that those FMJ DG. When comparing both, when shooting, the DG seemed slower. I don´t have a device to measure the speed, but I can see in bare eye that they are slower. I thought the penetration would increase due to the extra weight and the thinner diameter but no!!!! My CE out penetrates the DG by 1 inch!!    

On Stu's calculator, the DG has more mass, less speed, aprox. the same FOC but less energy!?

Is there a top limit in mass from which the energy does not increase, for the same set up? What this tells me is that increasing mass does not always mean the I'm gonna get more penetration. Does it make sense?

What's your thoughts?

Thanks
Diogo

[BowDiddle]

Yes, and yes it makes sense.

There will always come a point of reducing returns.

[Friend]

With a well tuned arrow, mass increase will provide greater penetration. If there is a point which mass increase vs velocity reaches marginal utility, it has yet to be defined. That point, if it exists, would be far beyond what one would consider reasonable trajectory in order to effectively shoot with competency.

There are numerous variables that may be yielding your results.

May wish to consider referencing Dr. Ashby's report where he takes a 40# recurve and a well designed heavy...heavy arrow(~18 gpp) to both effectively and consistently penetrate Asiatic Buffalo.

Just a simple analogy:
Damage incurred by being struck by either
... a baseball travelling 100 mph
or
... a 100 car train travelling 5 mph

I will take the baseball and hunt tomorrow.

[Fletcher]

No single factor will affect penetration nearly as much as arrow flight.  Any deviation from straight flight will greatly reduce penetration.  I suspect that the DG arrows aren't hitting the target quite as straight as your CE's.  

You didn't mention what type of target material you are shooting into, but differences in friction coeficients between the shafts and target will have a noticeable effect as well.  Penetration comparisons between foam type targets and animals are irrelevant.

With the DG's weighing 75+ grains more, they will fly slower from the same bow.  How much slower depends on the bow.  Ashby studies have clearly shown that momentum is a much more relevant factor than energy with relation to penetration.  Tho related, energy squares the velocity making velocity a much stronger component in the value, hence the lower energy value with the heavier but solwer DG arrows.

[Mitch H]

While there are many variables that dictate energy, as long as an arrow is properly spined and tuned for the bow being used there is no magic number where additional weight becomes detrimental to energy…….kinetic energy or momentum.

As long as the bow being used is capable of launching the arrow heavier always creates more KE(slightly) and more momentum.(more than slightly)

The ONLY way to accurately measure KE and momentum is to……

1. Make absolutely sure the arrows being tested are in fact tuned for the test bow.
2. Have an accurate chronograph.

As long as those two steps are met, you will always see small gains in KE as arrow weight increases, and larger gains in momentum. And as Fletcher stated, using a foam target is not an accurate representation in penetration as it pertains to animals.

[tecum-tha]

Waht did you shoot at to measure penetration?

[JimB]

It has already been mentioned but tuning could make the difference.There really isn't enough information to make an educated guess.If you are shooting both from your bows,the .300 FMJ would be way too stiff with only 200 grs on the front.An out of tune arrow will waste a lot of the bow's available energy and the only way to be sure it is tuned to that bow is by bare shaft testing.

[snag]

And so the pendulum swings back and forth.....light to heavier, to heavy, to really heavy, then for some back toward the middle. The wheelie crowd is experiencing this now. They went "tooth pick light" in order to chase the mighty speed factor and are now talking about heavier and FOC. There is a happy middle ground. Like the baby bear said, not too heavy and not too light...but just right!          I will sacrifice some weight for better tradgetory.

[parshal]

Interesting timing on this thread.

I took my Tall Tines to an indoor range the other night.  It was the first time I've been able to shoot at 20 yards.  The bow has two sets of limbs at 45 and 51#.  Both limbs have been tuned at Rocky Mountain Specialty Gear (in other words, not by me!) and turned out to be 11.2 GPP each.  They shoot 170 and 172 FPS as well.  So, for all practical purposes the should shoot similar or so I would have guessed.  Not so.  The 51# limbs have no discernible drop while the 45# limbs drop like a rock.  To be fair, I've shot the 51# more recently so I need to adjust to the 45's but I was amazed at the drop when both arrows are similar speed and GPP.  I figured trajectory would be the same.

This has to translate into more penetration for the 51#.

[Tav]

I built a spreadsheet that compares KE, Momentum, block velocity on impact, the impact force to stop an arrow in 24", and the height a block travels after impact.  All a 1lb block.  I used Stu's calculator and entered arrow weight and used his calculated velocities to enter into the spreadsheet.  The only problem with these calculations is that it doesn't reflect what happens after an arrow is inside of an animal which requires a whole new set of equations and assumptions.  Bottom line, 624 grain arrow was at 175fps and the 707gr arrow was 165fps.  For the FMJDG, the block will go 0.84" higher from impact which means it hits harder of course, and the impact force to stop the arrow within 24in is .33lbs more.  The difference in momentum was .0341bf-s.  After going through this exercise and then listening to guys who actually kill a lot of animals with our choice of equipment I learned that it is more important to worry about how sharp your broadhead is and how well your arrow flies.

[Shawn Leonard]

I agree with Snag, I shoot 8-9 gpp for all my hunting, I like an arrow going 180-190 fps. I shoot that the best and no need for more weight as I hunt in NA only and that will kill anything in North America including moose. I believe OL Adcock said once ya get to 15 gpp the efficiency of most Bows starts to decrease. Shawn

[Shawn Leonard]

I agree with Snag, I shoot 8-9 gpp for all my hunting, I like an arrow going 180-190 fps. I shoot that the best and no need for more weight as I hunt in NA only and that will kill anything in North America including moose. I believe OL Adcock said once ya get to 15 gpp the efficiency of most Bows starts to decrease. Shawn

[LittleBen]

I'm going to avoid anything to do with penetration or speed or "KE vs Momentum is better" because its been beaten to death and it seems to be more about faith than anything else.

To address the question here.
"On Stu's calculator, the DG has more mass, less speed, aprox. the same FOC but less energy!?

Is there a top limit in mass from which the energy does not increase, for the same set up? What this tells me is that increasing mass does not always mean the I'm gonna get more penetration. Does it make sense?"

I will address the question of energy only and not penetration. From an engineering perspective, increasing mass will always increase the energy.
The reason energy always increases is that the efficiency of the bow is higher at lower speeds. The faster the limbs move the more internal friction, the more the air in front of the limb resists the movement of the limb (same goes for the string).
Energy will not start to decrease at 15gpp, it will continue to increase, but the change in energy becomes smnaller and smaller as the weight increases. This link provides data regarding tests done on a compound bow up to 20gpp. The principles of energy storage are the same, despite the differences in bow type.
 http://archeryreport.com/2011/02/bow-efficiency-care/

As for Stu's calculator, it is an estimate, and clearly it is not particularly accurate under those circumstances. The heavier arrow is definately slower, it's probably just not quite as slow a Stu predicts. The energy transferred to the heavier arrow is certainly higher, probably not by more than  few percent though.

At the end of the day: 10% difference in arrow weight probably means almost nothing in real world performance. A good shot always beats a bad one, and a smart shot always beats a stupid one. Both those arrows are more thn heavy enough. Some will tell you go heaveier, some will tell you go lighter ... I say if anything just stay where you are and focus on going cheaper, that way you can go more.

[Orion]

As some have suggested, tuning, or lack thereof, could explain your results.  The Axis .300s are much heavier spined than the Heritage 250s.  I expect the arrow flight just isn't as good with them.

[ursusmajor]

I think snag hit it. There's gotta be a happy medium. I don't wanna b able to outrun my own arrow. Perfect flight so all of the bows energy is right behind the nock.
I also think there has gotta be some correlation between speed of sound, speed of the arrow, an animal's reaction time and how it affects shot placement.

[suburbanirma]

Dan Brockman did an informative article for the Spring 2013 TradArchers' World magazine that shows data/calculations for arrow weight vs KE and momentum when different arrows are shot from four different bows. You can check it out when the mag hits newsstands or arrives at your door.

[calgarychef]

Yup, it all comes down to arrow flight.  There no way those FMJ's are going to fly well in that configuration.  Mass, momentum all the hocus pocus goes out the window if the arrows don't fly we'll.

[Friend]

This particular response focus is not designed to offend – yet the bi-product maybe such- but to highlight the frustration incurred by those which have posted an inquiry. I, myself have been guilty of more than imposing a belief rather than offering a suggestion.


It never fails to amaze me when someone asks a specific question and the thread responses have little to no relevance.  Then others jump on the band wagon and the subject thread is thus hijacked.

One could have then responded to this virtually hijacked thread:
TG has a member that has harvested ½ dozen moose and black bear and an Alaskan grizzly utilizing a 50# bow in conjunction with a 9 gpp arrow. – While true -No relevance to the subject in question

TG has a member who was persistent in utilizing a 9 gpp arrow for polar bear.  Several pleaded that it was a very poor decision. He was successful. – While true -No relevance to the subject in question

Was a statement referencing Mr. Adcock’s position on GPP.  I am an ardent fan of Mr Adcock and have maintained an O.L. file of several of his TG responses.  Mr Adcock has been had passionate proponent of Dr. Ashby and Mr. Adcock’s GPP comment was prior to the 40# recurve-Asiatic buff study. –Still no relevance to the subject in question


Often we pick and choose information since it is what we wish to hear. Some may hang their hat on the GPP comment by Mr. Adcock and totally disregard Mr. Adcock’s comment that the perfect arrow design would have all the wt up front.-Still no relevance to the subject in question

Our Trad Gang family member from Portugal maintains both a commanding and unquestionable right to choose a 700 gn arrow and is entitled to answers pertaining to the direct subject in question.

[bowhunterportugal]

Thank you all for the time you took to reply my thread. Sorry not answered sooner but for the last 3 hours that I'm stalking some wild boars at night. Didn't got the chance to shoot but it was real fun.

Just to get some things clear:

1 - The arrows where bought to a compound shooter. Because they have a stiff spine, and before he tuned the arrows for his compound, I asked to shoot them to see if those would be a good substitute to my CE since the company that used to make 100 grain brass inserts for the CE stop doing them. So, I did the bareshaft tuning and they fly just great. They are 32" long, uncut. My CE are cut at 29" and also fly straight.

2 - I was just curious about this eye naked result. I shot both arrows to the same target (foam) and that was the result. I know it doesn't mean anything but maybe I was expecting those DG to pass right trough that foam...

I'm aware there are plenty of things that influence penetration. That's not what I was trying to know. Because I saw those differences in penetration and when I looked to Stu's calculator data, I got curious. Now I understand that it might exist a top weight from witch the data reverses but it is way over these 700's values.

Very interesting all your answers. Thanks for the teachings.

All the best
Diogo

[calgarychef]

Having retread all of the responses I fail to find ANY that don't have relevance to the original question.