Here's some numbers that may be of interest. Under bow1 and bow2 the orangish colored cells are results the white cells are input. bow 2 only allows you to change mass, peak weight draw and brace. I only changed from a 530 grain arrow to a 330. You can see that KE dropped by 5 ft/lbs but velocity increased by 46.3 ft/sec. In this scenario even the lighter arrow launches with 52 ft/lbs which is more than enough for whitetails. Of course arrow choice is a subjective thing but in this case anyway I would go with the 330 grain arrow.

Sylvan , your dead on , correct sir . It is relevant if you plan on hunting Africa , They want you to have a certain ke , or you cant hunt there .

True , the greater the ke , the heaver the arrow , for the same set up . It maybe only 4 lbs of energy , but its 4 pounds less with the lighter arrow . That was the original posters question .

Sylvan , you are correct sir .
True and the 4 lb gain comes from the heaver arrow , the original posters question . It is relevant if you want to hunt Africa , they have minimum ke requirements .

Sylvan , you are correct

Ture with the greater ke , coming from the heavery arrow . And that was the original posters question . In africa it makes a diferance , as the have minimum ke requirements .

Im haveing some trouble posting , if this reply shows up more than once .

The discussion of momentum and kinetic energy in archery is almost a silly thing to get too cranked up about. First of all it isn't like KE and momentum oppose each other. They go together even better than peas and carrots. If you do something to increase KE you will by default be increasing momentum as well. If you do something to increase momentum you will by default be increasing KE. For all practical purposes, in archery they are inseperable and virtually indistiguishable. Are they different? Yes, but if you truly want to understand the difference I suggest you get a book on mechanics and do some studying because there is a lot of misinformation regarding this subject in these forums.

The real reason for the discussion comes down to the question of what weight arrow to choose. The facts surrounding this decision are actually pretty simple. Shot from the same bow, all other things being equal heavier arrows will stike the target harder and they will strike it harder at all practical hunting distances. Your bow will probably shoot a bit quieter too. Unfortunately the arrows will travel slower and therefore follow a larger arch. So there you go, like with many things in archery its a tradeoff.

Although heavier arrows always mean more punch there comes a point of diminishing returns. Now it is arguable as to what the minimum amount of ke or momentum is needed for a whitetail but once you have made that somewhat subjective decision it doesn't make a lot of sense to exceed it by a whole lot. If you do then the excess energy/momentum gets wasted in the ground after it has passed through the animal.

If you strike a whitetail deer in the kill zone with anything over 35 ft/lbs KE or if you like to talk momentum then say 0.4 slug ft/sec then it is likely you will find your deer and probably not too far from where you shot it. If you gut shoot a deer with 100 ft/lbs of KE it will live for quite a few hours and potentially travel quite a distance.

SOMETHING STRANGE IS GOING ON HERE!

I notice your chart conveniently omits momentum readings and downrange energy. For momentum, the 530 grain arrow will carry .5170 lb/sec at the bow and strike the target at 30 yards with 53 ft lbs of energy (1 ft lb more than the 330 gn arrow has at the bow!).

The 330 grain arrow carries only .3892 lb/sec at the bow and has dropped off to an anemic 46 ft lbs of KE at 30 yards.

The idea behind light arrows is to get flat trajectory to make up for misjudging yardage at long range. Okay, let's look at the KE/momentum numbers for these two arrows at 50 yards.

The 530 gn arrow gets to 50 yards still carrying 51 ft lbs, only 1 ft lbs less than the 330 grainer had at the bow! The 330 grainer arrives with a mere 43 ft lbs of energy. Momentum? The 530 gn arrow has .4907 lb/secs at 50 yards. The 330 grainer has .3556 lb/secs.

It doesn't matter whether you believe KE or momentum best predicts penetration potential. The heavier arrow wins on both counts.

The light arrow thing is trying to balance the flat trajectory with still having enough oomph to keep the arrow from bouncing off the animal when it gets there. Is 330 grains enough? Maybe, but I wouldn't risk it. That kind of thinking, though, is why I am so much in favor of establishing a 400 grain minimum for hunting arrows.

Well, I don't know what happened to my post. Went into some secret internet dimension I guess. But the gist of it was along the lines of what Sylvan said: The fact of the matter is, light arrows lose out on all counts. The lighter the arrow, the less efficient the bow is, the less momentum the arrow has and the less energy the arrow leaves the bow with. The only thing going for them is the flat trajectory to make hitting game easier at long distance. But then, what happens to performance out there at long range?

In the example used above, the 530 grain arrow carries more momentum which helps it retain it's energy better on it's way to the target. It will actually strike the target at 50 yards with 51 ft lbs, only 1 ft/lb of energy less than the 330 grain arrow has at the bow! The 330 gn arrow has let it's KE dribble down to a measley 43 ft lbs.

Is it a big deal to worry about downrange performance when you're talking deer hunting and cranking out 70-80 ft lbs of energy? Probably not. Is it a big deal when you're shooting a bow that just barely the legal minimum draw weight for hunting? Not only is it a big deal to worry about downrange KE and momentum, it's CRITICAL!

I am very much in favor of establishing legal 400 grain minimum weights for hunting arrows.

After reading all 4 pages of this post, I still haven't seen the formula that was taught to me in my college physics class.

The formula for kinetic energy is 1/2 mass X velocity squared.

Mass and weight are technically different but it is considered the same in this formula. (it is different in space with zero gravity)

Velocity is your feet per second FPS.

Back a ways in this post, someone wrote that speed is more important. They are correct, because you multiply the speed by itself which increases its value A LOT.

On the other hand, the weight is less important because before you multiply it with the speed, you cut it in half.

Let's consider an arrow that weighs 500 grains and flys at a speed of 200 FPS. You multiply 200 times 200 and get 40,000. You then multiply this times half the weight which is 250, and you get a VALUE of 10,000,000.

Now let's consider an arrow that weighs 300 grains, BUT flys 320 FPS. 320X320=102,400
Then multiply this 102,400 times half the weight (150) you get 15,360,000!

This is an increase of more than 50%

That is why speed is more important than weight when it comes to KINETIC energy.

I am in NO way saying that the only way to go is to use lighter arrows, I am only giving an example of how to find kinetic energy in a bow. I am also not saying that a heavy slower arrow won't kill deer, this is only here to teach how to find the kinetic energy.

I just spent thirty minutes typing a reply, and it disappeared!!