I was tinkering around and did a search on this topic... I didn't have a chance to read all posts, but most... Some very interesting thoughts on KE relating to momentum and penetration...

One thing that I think needs to be mentioned when trying to relate KE to Momentum is that we are talking about the speed at impact NOT the speed leaving the bow (which is where everyone is testing on chrono's). The difference in KE to Momentum is greatest at first, but will become closer the further the target is from the point of release. The reason behind this is that a heavier arrow will loose more velocity than a light arrow due to gravity.

That being said, you can't say a heavier arrow will out penetrate a lighter arrow. If KE is the same, a lighter arrow will out penetrate a heavy arrow at a certain point downrange (the velocity difference will eventually even things out and turn momentum in favor of the lighter arrow). This is dependent on how far the target is from the point of release. The heavy arrow will loose velocity quicker, thus the momentum will decrease. The point at which this happens I do not know. I plan to test velocity at various yardages to see the downrange velocity differences with various weight arrows.

For example...

1) 400 grain @ 270 fps (65 ft-lbs. KE) Momentum @ release = 108,000 grains * ft/sec

2) 450 grain @ 255 fps (65 ft-lbs. KE) Momentum @ release = 114,750 grains * ft/sec

In theory Momentum is higher on set-up #2 - largely because we are calculating at the point of release...

@ 20 yrds. if #2 drops to 160 fps and #1 drops only to 180, the momentum on #1 and #2 will be equal at the point of impact. I think KE may actually be a very good gauge for actual momentum and penetration. It depends largely on how much speed difference is seen downrange. I plan to test down-range velocity to see how much greater the speed loss is on heavier arrows. There should be a point downrange, where the increase arrow weight reduces velocity enough to where the lighter arrow will have higher momentum.

dw
take a look at siskiyou's post a couple of pages back. A heavier arrow will actaully hold it's speed better than a lighter.

On that note, of a heavy arrow holding it's speed better than a light arrow...

The club has a 3D target set up at around 120 yards or so that we lob arrows at for grins. I had the gap figured out with my 2315's. Hold where the bow's shelf is right on the top line of the target and the arrow drops right in. Now, with the carbon arrows that I just started shooting -same length, same 3-under fingers style, same anchor, same poundage, 4" plastic vanes instead of 5" feathers, 130 grains lighter and 25 fps faster out of the bow - they fall nearly 20 yards short of the target with that same gap.

I noticed the same thing in the 80's when I tried switching from 2216's to 2213's for field archery. My pin gaps between 30-40 and 40-50 got a little narrower while my pin gap between 50-60 and all my long distance gaps got much wider. According to what I've experienced, which is backed up by ballistics programs, past 50 yards light arrows start running out of steam, real fast. Not very applicable information for hunting, but it does show how much a little more weight helps hold energy downrange.

Okay, I was off on that apparently... Higher intitial momentum must keep the speed up above that of the lighter arrow with lower initial momentum - even though gravity is playing a larger role with the heavier arrow.

Thus, KE isn't a good gauge. Momentum (even intial momentum at release) seems to be a better gauge for hunting/penetration purposes than KE... Why bother calculating KE and not use momentum? The energy in the arrow at release is not a real good gauge. I'd rather calculate momentum and know that the higher initial momentum will penetrate better at any range. The other key factor is that your bow efficiency will most definitely increase with a heavier arrow - more potential energy transferred into KE and less lost potential energy.

Just between you and me and the fencepost, speed with light arrows is what's selling bows, it's what's popular now, and KE correlates better with speed than momentum does. Many people don't at all care to be reminded that guys shooting longbows with wood arrows and cut on impact heads are zipping thru elk and moose with only 40 ft lbs of energy, but with arrows weighing between 10-13 grains per pound of draw weight and carrying high momentum. Why not? Because it doesn't fit neatly into their rationale for shooting very light arrows at 5-6 grains per pound, as fast as they can, at animals.

But watch the forums over the next few weeks. We'll start seeing many variations on the question, 'why didn't my arrow get good penetration?' and I'll still be hanging around saying 'try a heavier arrow.'

I still say that arrows in the 7-8 grains per pound range will give better penetration than lighter ones, regardless of what material they're made out of, without sacrificing all that that much in speed or trajectory. A little less speed for a little more energy and a good bit more momentum. It's a good compromise, IMO.

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Just between you and me and the fencepost, speed with light arrows is what's selling bows, it's what's popular now......Why not? Because it doesn't fit neatly into their rationale for shooting very light arrows at 5-6 grains per pound, as fast as they can,....
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Very nice Arthur!
The speed means less drop and less drop means higher scores during 3D shoots because you don't have to be as precise in range estimation!

The other factor you mentioned ... &quot;at animals&quot; dosn't even come into play as that isn't a primary thought with most of these bows.
Hunting set-up is a secondary concern these days. I shoot what I shoot because I hunt. I shoot 3D for hunting practice plain and simple.
I also know I am in the minority with you in a quite &quot;slow&quot; effective set-up




Greg

&quot;Getting close to the game is the joy of Bowhunting for me, the harvest is a bonus.&quot;

Live 15 ft Python after eating a small Antelope!

I am not sure that gravity will slow the heavy arrow faster...it (gravity) is only trying to get the arrow to move in the vertical plane (arrow drop). But a heavy fat arrow will have a very similar effective specific gravity as the light skinny arrows. Even at the extremes, you won't find the light arrows to fall to the ground any faster than the heaviest arrows.
The force we need to deal with is wind resistance (cg). For all intents and purposes, arrows have a similar cg. Hence the arrow with more momentum will fight the wind better. Wind it the only force trying to slow the arrows, not gravity. Gavity only wants the arrow closer to earth. Being that the cg of most all arrows is similar, the one with the most momentum will keep it's speed longer.

I think some of you need to go back and look at my speed and ke of light arrows verses heavy verses carbon.The lighter smaller carbon will hold more ke and speed downrange than a heavy arrow.Yes if all things are equall,then a heavy arrow will hold more ke but equality is rarely achieved.The smaller arrow will almost always outperform a fat aluminum downrange.Problem is that smaller isn't always better for fixed broadheads,therefore the need for mechanicals.





Hey Arthur,I can't believe it,your coming over to the dark side.I would like to know how the spine holds up on those Epics.Seems that would be the only for possible problem for you.

The funny thing is,I put a weight tube in 1 of my Stinger and a 100 gr point and have it up to 440+or-grains.I have it in my quiver and plan on using it in extremely thick areas.Weight is always better in the thickets.This arrow actually shot thru my board with my new hunting bow where without the weight tube it was hanging on the fletching. <img src=icon_smile_shock.gif border=0 align=middle>


The real funny thing is hits the same or VERY close to the same as the lighter ones out to 30 yards.It is 20 fps slower.Kind of proves what we say about speed being overated for yardage estimation.



I had aready forgotten about this thread and had moved on.Can't believe it is still going.

Oh yea,gravity is the same wether it is a golf ball it is pulling against or a bowling ball.The only difference is the amount of resistance.

There is a cool trick you can do with a book and paper to prove this.Paper falls at the exact same rate as a book.All that you need to do is put the paper on the book and drop the book and they will not come apart.This is just keeping the resistance the same.

Well, TFOX, I haven't burned my LOLF (Loyal Order of Log Flingers) card just yet. Frankly, I'm half P.O.'d at these carbons tonight. Went out to the range with a half dozen for our weekly fun shoot. Came home with 3 shootable arrows left in my quiver. Pulled 3 inserts out of the blasted things.<img src=icon_smile_angry.gif border=0 align=middle>

We have a couple of targets set behind a screen of thin brush. I didn't quite get through the hole I was aiming at clean. Clipped a tiny twig, about 1/16&quot; in diameter. It glanced my arrow out of the kill, into a gut shot on a javelina target that is about 6 yards beyond the brush. Of course, on another shot, one of our members shot a carbon arrow that went straight through a hackberry sapling about 2&quot; in diameter with a carbon. I'm talking complete passthru and sticking in the target beyond. Difference between a glance off and a solid, direct hit.

So, if you do mess up and hit a bone in an animal, it appears you'd better hope it's a solid, direct hit instead of glancing contact.

Thanks for posting your point of impact results with that weighted carbon. It's nice to have someone finally do their own experiments and come up with independent information that corraborates my own experiences. If you could, how about setting an 80 yard pin with your unweighted arrows and then try the weighted one? I think you'd be interested in what you find.

Hey, someone had to have the 250ith post to this subject
TFOX, I think we are agreeing to an extent. I am only saying that basically, all else beign equal (shaft diameter, fletching, head etc) the heavy arrow keeps it's speed longer.
The skinny carbons will have a lower cg and that will make up for last of momentum vs the wind.
&quot;The archery program&quot; shows that a 450 grain arrow shot out of a test bow starts at 235 fps and after 100 yards slows to 189fps
The same bow shooting a 350 grain arrow starts at 267 and drops to 202
The light arrow is doing 220 at 70 yards, the heavy one 220 at 30 yards. Starting with both arrows at the same speed (220) the heavy one slows to 180 fps in 90 yards the light one slows to 180 in 70 yards. At 30 yards, the lighter arrows will hit about 2&quot; higher.
I think we can agree that ALL else being the same the lighter arrow slowes faster....if we want, I'll check the results of same weight but different shaft size arrows (and or feathers vs. vanes)

Edited by - Stealth_Force on 09/06/2002 03:29:03