dsheally

You and I both know that Pro shop owner was wrong on that statement Cougar Mag.

NonServinam

Hi
Here are some info I found, (speed and KE).

Bowtech Patriot set for 28" draw length and 60# draw weight
300g Arrow (5 g/p/p) 273.0 fps 49.66 ft-lbs of KE
600g Arrow (10 g/p/p) 201.6 fps 54.16 ft-lbs of KE

LOSS of Velocity: 26.2% GAINS in KE: 8.3%

You dont gain so much with a heavy arrow if we talk KE, and I dont know how much more penetration you get. But if you don´t know the distance to the target u will have an advantage with a faster arrow.

//S

burniegoeasily

Force = mass * acceleration.

Keeping every thing starting with the same initial force, then the force generated should be equal. As for penetration, lighter arrows could absorb some of the impact force in its matterials as well as some of the initial force (elastic response). So as an assumption, too light will not penetrate as well. You need to find the mid line you are comfortable with.

Bulzeye

While I certainly see the value in lightest, fastest arrows for flattest trajectory, I've always leaned on the 'heavier is better for penetration because of the greater momentum' side, but it was just a gut feeling, not factual.
(I'm just now becoming aware of KE and how everything relates to it, so take all of this with a bucket of salt.)
Shot placement has always been my thing.

I read an interesting article on penetration by Dave Holt, Technical Editor of Bowhunter Magazine (Dec 2003).
The guy seems absolutely maticulous about his scientific methods and sounds like he knows his stuff.

Among other tests comparing cut-to-tip heads and ferruled point heads, he also shot 2 arrows of the same KE, length, diameter, with the same broadhead, but with weights that were 200 grains different (400g and 600g). So, given that, as he explained it, they had the same KE, but different momentum. To my surprise, they penetrated the same distance in a homogenous target, indicating that, at the tested distance of 16 yards, KE was the key factor in determining penetration, not momentum. Not what I expected, nor do I know if he missed something, but it was an interesting read.

So, I'm confused. [:@]
...and I see the debate rages on.

Good luck with it, I'm going to the range.
-Bulz

burniegoeasily

That right there is the most important. You can shoot a deer with a long bow with a lot less KE and as long as the shot placement is right, it will kill that deer as well as a hopped up compound. Just got to get it in and in the right place. Indians were killing them with spears and weak bows well before compounds came around.

KEM

Everyone is accurate in their statements on this one but let’s add science. Two factors come into play for penetration. Energy prior to impact and friction force between the arrow and the target. Let’s start with eh easiest to quantify the KE

Kinetic Energy of a projectile is calculated as follows

Mass (in grains) * Velocity (in ft/sec) * Velocity (in ft/sec) / 450,240 = Energy in Ft*lb

Now say you shoot both the arrows at say 260 ft/sec the energy is 41 ft *lb versus 60 ft*lb in the heavy arrow, or 60/41= 46% more energy in the heavier arrow. Realistically the heavier arrow is slower so let say you get 260 from the lighter and 240 from the heavier. You now have 41 ft*lb for the lightest and 50 for the heavy or 50/41=22% more energy. As these get closer the penetration will become similar for the same arrow.

Now the hard part friction. While several factors affect friction consider the two largest, material smoothness and surface area. As big bull stated correctly two arrows one skinnier than the other the skinnier presents less material in direct contact with the target and therefore can penetrate deeper. The wider the diameter the larger the area in contact.

Let calculate total possible area exposed for two arrows.
Total area = 2*3.1415*radius*length of arrow= inches square total shaft area
The diameter is (for alum) the first two numbers divided by 64 i.e. 2219=22/64" OD
For a 2215 versus a 2315 you have approximately 5% more surface area per inch of penetration or for a 25 inch arrow 28.2 sqin versus 27 square inches.

Finally you have the smoothness factor. A smother arrow will penetrate deeper. The science behind this is too long to detail. So take my word. What you have is however a simple comparison. The weight of the arrow plays the biggest role in penetration followed by shaft diameter or friction (these can easily swap as to which is more important)

I TOLD you it was not a simple answer

Now comes the non academic answer which I prefer.
Why ask the question when you can easily make up two arrows and test it out!
Use the same arrow length and diameter and just load some silt, salt or sand to make the weight difference up. (Accuracy is obviously not part of the bet.

A bit of a ramble but there are always details people forget to quantify.

BobCo19-65

What exactly doesn't matter? What if I decided to put a 2 3/4" diameter mechanincal using 50# on the light weight arrow?

silentassassin

I saw woman on video shooting goldtips and a whisker biscuit get a pass through on a big bull elk a few years back. Just thought I would throw that in.