K.E. VS Momentum

[BT]

Here is the truth of the matter on the arguement of K.E. verses Momentum.

On the other end of the argument is the long range results.

I have no physical evidence of this (like I do here) but none the less , the results are in the extreme diffrence at ranges of 80yrds. when favoring the heavier arrow.

Since I am not shooting 70+yrds. , I could care less soooo....[]






Kinetic energy plays a major role in penetration.

A lighter arrow will, through increased velocity, maintain nearly the same level of kinetic energy as a heavier arrow.

Example: Reducing the grain weight of an arrow by 100 grains will only reduce kinetic energy by 5% or less.

On one hand there is the Momentum gain over long distances and thats a true enough statment but then there is the advantage that the lighter arrow still carries in yet a diffrent way.

Since the sight window on the lighter arrow is still smaller , the lighter arrow still has less best chance of hitting the target area if the yardage is guess incorrectly.
(to a degree)

The same weight that adds to the momentum side of the therory adds to the sight gap as well.

Therefore....if you want to have the added power of momentum , you have to choose your yardage better.

200grns.effectivly changes the sight picture roughly 7" over 50yrds.....enough to miss a deers entire vital area

If I simply choose a better entrance (away from the shoulder)I dont have to worry about the miss/wound at that range.

For example....with a 500gr. arrow my BK2 will shoot flat to 23yrds. before breaking out of the 3" ring and I will need just over 2 pin heights to hit that same ring at 50yrds.

With a 300gr. arrow I will need 40yrds. to drop out of the 3" ring and need just over 1pin height to hit that same ring at 50yrds..

So...with the lighter arrow,my only job is to select the correct aiming point whereas the heavier arrow also carries the burden of needing to know my yardage perfectly just in order to hit the target.

K.E. will drop in relation to speed so that is out.

On the other hand...Down range Momentum is a fact of life

This is where the lighter arrow V.S. heavier arrow debate should really be focused.

A heavier shaft will not have as much K.E. as a lighter shaft since speed drops off in a greater amount than the percentage of weight added.

Depending on the arch of the arrow it is indeed possable to have an arrow impacting with more force at a greater distance than it would have at a closer distance where K.E. is already diminished.
But...not at a point of zero where the total energy/Mass is intact.

If you really want to know just get a bag of play sand and shoot into that


IMHO
_________________
Think with your head....not your heart!

[rreda]

On stand the other night, I did something dangerous, I started thinking!

I started to wonder if all Kinetic Energy was equal? This was my thought process. Let's say you have two different setups, one with a lighter arrow, and one with a heavier arrow. But due to the other variables, both setups have the same K.E. on impact at 25yds. If an arrow shot from both setups was to hit the nearside scap, would both arrows get the same penetration, or would one have an advantage? My gut tells me that the heavier arrow might get better penetration, but I am just guessing.

Thoughts?

[smj]

Seems like that would be an easy one to set up. Probably two bows, tune them to shoot different arrows of different mass yet maintain equal KE at 25 yards - same tip as well. I suppose one question not addressed would be arrow spine and what it contributes to penetration. You would also need a target that niether bow could shoot through, so you could measure the depth of penetration, and consistant resistance throughout. I am sure BT can tells us what I've missed here!

[rreda]

I had not considered the arrow spine, but you are right, it might make a difference due to vibration etc. It is just treestand musing, but I would be interested in know the answer.

[Pete]

BT, correct me if I'm wrong but it sounds like your main point is we should (or could) shoot lighter arrows without any loss of noticeable K.E. Why do so many bow hunters shoot heavier arrows then? I shoot CX 6075 Terminator Selects @ 29" w/ a 100gr. Sonic broadhead. They weigh approx. 420gr. With most of my shots being 30 yds or less, besides being able to use one pin, what are some advantages of shooting a lighter arrow? Aren't heavier arrows quieter VS. lighter arrows?

[BT]

rreda said:

Let's say you have two different setups, one with a lighter arrow, and one with a heavier arrow. But due to the other variables, both setups have the same K.E. on impact at 25yds. If an arrow shot from both setups was to hit the nearside scap, would both arrows get the same penetration, or would one have an advantage?

The heavier arrow would have the better penetration due to the added mass if K.E. values were the same.

[BT]

ibohunt2 said:

BT, correct me if I'm wrong but it sounds like your main point is we should (or could) shoot lighter arrows without any loss of noticeable K.E. Why do so many bow hunters shoot heavier arrows then? I shoot CX 6075 Terminator Selects @ 29" w/ a 100gr. Sonic broadhead. They weigh approx. 420gr. With most of my shots being 30 yds or less, besides being able to use one pin, what are some advantages of shooting a lighter arrow? Aren't heavier arrows quieter VS. lighter arrows?

Most people shoot heavier arrows because they are following a group mentality that dictates weight allows better penetration.

while weight may add to penetration it is in almost all cases a marginal gain that needs to be seen under lab like conditions to be appreciated.

That is to say that you'll never tell the difference in real life when you hit that deer

That is when we are talking about the first half of the trajectory curve.

Traditional archers have alot more advantage with the high mass arrows since they are nearly always shooting past the curve

Of course...there are trad. guys out there who never shoot past the curve and they would do just as well with the lighter/faster arrow.

Why dont they then?
Could be that it's because the heavier arrow is easier to control off the shelf than a lighter arrow

But back to the compound...

The biggest advantage is (as you mentioned) flat trajectory.
Another advantage (if you use it correctly) is that you will gain the advantage on a deer as to the string jumping.

This is to say , if you have a deer jump the string on a bow shooting 250fps @ 15 yrds. the next time he will be dead if that same shot comes at him @ 300fps provided we are aiming the bottom 1/3 of the body.
(This is gone over in judgment call)

BUT!....Speed does not help that much at all
a 50fps gain only allows about a 2 yard advantage on a deer that string jumps.

Still in all .... 2 yards is 2 yards

The faster arrow also allows for a smaller window in our 10yrd. pin gap.

On my bow , I have an 8" window between 40 & 50 yards which means that if I hold the 40 yard pin dead center at 50 yards the arrow will strike the bottom of the lung.

This allows for alot of error in judging distance~!

When I went to 12gpp on the same bow my shot window climbed to 14" on the same 10 yard window.

You can see how that would have effected me

Rule of thumb is 1" less window gap for every 25fps gained.

Lastly...
Yes , heavier equates to quieter but I am a firm believer that there is no bow quite enough to escape a deers attention.

A deers attention & demeanor dictates reaction and if a deer is going to duck out then it will happen regardless of what your bow sounds like.

I have shot ALOT of deer with this BK2 and it is loud! ..... obviously the deer that didnt flinch were not going to and the ones that did were going to.

You cant change a deers reaction by changing your bow

[BT]

michihunter said:

So Tell me why Trad shooters consistently shoot heavier arrows?

Look above!

I personally feel there is a medium, where too much weight begins to become less efficient. IBO weight arrows are certainly faster but in my own opinion and from my own experience, a heavier arrow is the way to go. My reasoning is that impact reduces a lighter arrows KE much quicker than a heavier arrow allowing for more pass through.

I like the formula and deductions that 2chucks2 came up with to be honest.

I believe his logic was about the best I have seen on the subject.
(it also came very close to the findings on BowJacksons site)

Your contention that more weight drives forth with less loss of energy is true enough but at what point do we need more force?.

My performance with a 312grain arrow (total weight) out to 50yards has resulted in total pass through with a religious consistency.

I just do not see the need to reduce my flat trajectory to get even deeper in the off side dirt

[BT]

smj said:

Seems like that would be an easy one to set up. Probably two bows, tune them to shoot different arrows of different mass yet maintain equal KE at 25 yards - same tip as well. I suppose one question not addressed would be arrow spine and what it contributes to penetration. You would also need a target that neither bow could shoot through, so you could measure the depth of penetration, and consistent resistance throughout. I am sure BT can tells us what I've missed here!

Oh by the way....

I helped my son with a science project the year before last and it was a hit for all the bowhunting fathers
(he won 2nd prize)

we used a crossbow and a bucket of dead sand to test penetration differences between two bolts that weighted 160grains in difference.

The bolts were identical except that one was stuffed with a AFC shaft which bumped the weight.

We set up a cross that allowed the bow to be fired downward into the sand and then the bolts were measured out.

The test was done well over 100 times as each new viewer had to see the demo.
Each and every time the lighter shaft won by a wide margin.

I mean WIDE!!

of course this was due to the fact that there was no bleed off and it was going significantly faster.

That about sums up the argument.

As you increase the distance the margin of gain begins to deplete until it reverses and the heavy shaft no has the advantage.

[Greg Krause]

until 2 years ago i shot an aluminum that was over 600grains. Last year I shot a carbon coming in at 435grains and this year i am shooting 370 grains. I have noticed no difference at all in penetration. still having pass throughs even with mechs. Ray switched to the same 370 grain arrows and blew through the scap on a big doe at 17yds, leaning an exit up in her neck, using a spitfire. There is very little difference in noise from my trykon when using 488grain arrows or 370 grain ones. I lost about 1# of KE going to the lighter arrows but I gained speed, making my shots more accurate. Honestly if I were only hunting deer and less than 30yds I can't see an advantage to a heavy arrow, unless you are already low on the KE.