Kinetic Energy

MinnesotaHunter said:

Bow tuning also plays a role in penetration. You can do all the formulas you want, but if your arrow is not flying true, neither your momentum or kinetic energy will be focused behind the point of your broadhead, and will be wasted.

The science is interesting....

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I agree but would add that in general the heavier (slower!) the arrow the easier it is to tune and the more forgiving it will be to any slight flaw in form under actual hunting conditions. At least that has been my experience.

KE is the wonder number utilized by many as an indicator of the killing ability of a particular round vs. another. To some degree it can hold merit. It's heavily weighted toward velocity though. Bullets kill by transfer of energy and the resulting shock disruption to internal life systems. All fine and good ...with bullets.

But, arrows aren't bullets. Arrows kill by hemorrhage, blood loss. This is accomplished far, far differently than with a bullet. An arrow must 1st be able to penetrate into a vital area, and 2nd cut a sufficient amount of tissue to cause massive hemorrhage leading to the demise of the animal.

KE will only deal with the impact of the arrow, but nothing beyond that. Other factors take over rapidly. Here is where momentum starts to come into effect. Surface area of the cutting edges bear in on the equation. And finally.....a factor not dealt with in firearms....sharpness.

A sharp broadhead of moderate width, on an arrow of moderate weight, propelled at a moderate velocity will have a tendency to out penetrate a higher velocity, lighter weight, less sharpened arrow.

My first archery deer, some 40 yrs ago, went down with a cedar shaft and a simple 125gr Bear 2 blade broadhead shot form a 40# bow at 35yds. Complete pass through.

I'd give the vote to weight and sharp every time, and take the time to judge distance better, over faster, lighter and get a 1/2 penetration poke.

Gunner's $0.02 that you can try to cash in at any local coffee shop.

Am I the only one who sharpens my 55 gr fmjbt's for better penitration?

I like the test of shooting at different targets and seeing which one penetrates more. I shot a thin carbon arrow at ten pounds less than my friend with the bigger diameter aluminum arrow and mine penetrated more.

Momentum may be more important than KE, but actuall penetration is the way to settle the issue.

https://www.physicsforums.com/threads/momentum-vs-ke-which-determines-projectile-penetration.195119/

Save yourself the mathematic headache and shoot a heavier setup. I use to shoot a light fast setup on whitetails (325 or 350, can't remember). Anyhow, after a bunch of research I went to 425 gr complete with Eastons Full Metal Jackets and 125 Slich Tricks before my elk hunt.

After plenty of practice I have no interest in going back to the super light setup. It killed an elk and many whitetails since. My .02 is go heavy, and believe in momentum.

Tom said:

I like the test of shooting at different targets and seeing which one penetrates more. I shot a thin carbon arrow at ten pounds less than my friend with the bigger diameter aluminum arrow and mine penetrated more.

Momentum may be more important than KE, but actuall penetration is the way to settle the issue.

https://www.physicsforums.com/threads/momentum-vs-ke-which-determines-projectile-penetration.195119/

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I like this idea but the only problem I see is that (I think) most broadhead targets stop the arrow by using friction on the sides of the shaft and I think most elk stop arrows by friction on the cutting point. I maybe wrong?

Kinetic Energy is a mathematical calculation. You have the formula here a couple of times. Plug in the numbers and settle the discussion.

Please don't use the "this arrow penetrated deeper into my target" as an actual way of testing this. How do you measure the density of each area of your target to ensure consistency? A small diameter arrow should penetrate further than a larger diameter arrow because there is less surface area in which the target has to grab to slow the arrow to a stop. When shooting a heavier arrow you also have an advantage in windy conditions as more force will be required to deviate the arrow from its path. The amount of energy carried down range should be much greater for the heavy arrow.

MontanaWild said:

Please don't use the "this arrow penetrated deeper into my target" as an actual way of testing this. .

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Sorry, That was a bit tounge and cheek. Two guys sitting out in the garage arguing about whose setup is better.

That being said, how do you account for the additional friction of a 4 blade vs 3 blade vs 2 blade, or the cutting angle of the broadhead, or tuning?

I agree we should endeavor to set up our arrow as best we can, but at some point results matter.