question about arrow weight and speed loss
 

i was shooting thru the chrono w/ some 520 gr arrows at 240fps from point blank. my buddy was shooting 257fps w/ a 377 gr arrow at point blank. from 23 yards i was shooting 232 fps, he was shooting 243 fps. i lost 8, he lost 14fps. is this a percentage speed loss - or do heavier tipped (200 gr) and spined correctly arrows slow down - well, slower.

i didn't trust him to shoot thru the chrono from any further or we would have done that and i'd have some #'s.

RE: question about arrow weight and speed loss
 

I think it is that "momentum thing". The heavier arrows maintain more momentum over distances. Because they are heavier the "drag forces" don't slow them down as much.

RE: question about arrow weight and speed loss
 

Just pure physics. A heavier mass will retain a higher percentage of it's velocity over a given distance.

RE: question about arrow weight and speed loss
 

Cuz.

Refer to our many phone conversations on the very subject[8D];):):D

RE: question about arrow weight and speed loss
 

I was going to relate this story to Aussie last weekend at the show, but we kept getting interrupted by folks wanting to look at bows. The nerve of some people!;)

I learned about this difference in downrange performance a long time ago. I'd decided I wanted flatter trajectory to make it easier to hit that 70 and 80 yard target (NFAA Bowhunter Freestyle Limited class), so I put on a 5" overdraw to shorten my arrow to 29", enough to get from 2216's to 2213's. This is obviously PC - pre carbon. [8D]

I cut down some of my 2216's to tide me over until my new arrows were ready. I did have to close in with my 50 and 60 pins a little, but I expected that because taking the length down lightened them some. Made sense, lighter arrows/flatter trajectory, right?

Took my 2213's out when I got 'em, made a couple of slight tuning adjustments and sighted them in. My pin gaps between 20-40 tightened up considerably. But there was a huge gap between 40 and 50.[:-] The distance between my 50 and 60 pin was wider than it had ever been before.

With the full length 2216's, my pins measured 1 1/16" from the 20 to the 60. With the short 2213's, they measured 1 1/2". Not what I'd expected. Lighter arrows, flatter trajectory???? Something's not right.

Went over to the 80 yard target, did my normal pin stacking to get my aim point and I was horrified. My arrow didn't hit the spot. Didn't even hit the target. It stuck in the dirt 2 yards short of the target. I shot another 3 arrows, just to make sure. I had a nice 4 arrow group in that spot, 2 yards in front of the target.

Went back to the truck and got my shortened 2216's and went right back to the 80. Didn't move the sights. First arrow cleared the top of the target by a good amount. Changed to my 70 yard gap. Arrow stuck in the top 4 ring. Changed to my 65 yard gap. Spot! Spot! Spot!

Went and gathered up all my arrows, hauled my buns to the practice range and re-tuned/re-sighted for the 2216's and put a For Sale sign for a dozen 2213's on the club house.

The heavier 2216's shot a lot flatter at 80 yards, where I needed the flatter trajectory. My pins measured an even inch after I'd sighted back in with them. They were also evenly spaced instead of being real close for the first 3 pins and real wide for the last 2. Eventually I took off the long overdraw because it was a little too critical to shoot well with fingers and settled on a 2" overdraw.

That little experience is what got me really into this arrow weight/momentum/downrange energy retention stuff.

RE: question about arrow weight and speed loss
 

You have alot more energy being transferred into your arrow and that will equate into flatter trajectory.He has 55 ft/lb and you have 66 ft/lb,I believe is what I figured.You either have a longer draw or more poundage than him,right?


Arrow weight plays a role but the amount of energy you put into the arrow will directly affect how flat it shoots.


That is why most of the 3-d pros use bows around 65# instead of 55#.(I even know of atleast 1 that uses 80# only)Sure they can match the arrow weight to the poundage and get the chrono speed at the bow but the higher energy setup will yield in flatter trajectory.


This is why I had to get away from fat shafts,I didn't have enough energy to be accurate with them downrange.They lose too much speed too fast and become unstable and float on me.Basically,my groups opened up at distance with them.[:-]


Yes,heavier arrows do retain more downrangespeed.The reason you saw so much difference was a combonation of the 2.

RE: question about arrow weight and speed loss
 

i don't quite get that. w/ a chrono at pt blank we're dealing w/ an initial velocity - plain and simple right? the only acceleration we're dealing with is caused be gravity.by the timethe arrow is in the chrono there is no more horizontal acceleration. i don't believe it matters what the bow did, or if the arrows were thrown - i think bg's right - its harder to slow mine down. we're both shooting 29" draw, and our pounds were w/in 2. he had 4" fletchings on a slight offset and i had 2" blazers w/ helical and so offset the vanes are just barely on the shaft - and they won't quite get thru the nap 360 w/out one of the bases touching the launcher. (i over did it just a little.)

RE: question about arrow weight and speed loss
 

Higher energy equals more efficiency.You have heavier arrows and that equates to some of it but there is no way you will see that much difference in speed loss if you shot those same 2 arrows out of the same bow,not at 23 yards.

Think about it,he lost almost twice as much as you.

Try it,it won't happen.

RE: question about arrow weight and speed loss
 

John,

In your case it doesn't matter what kind of vanes are on the arrow when checking the speed out of the bow as there isn't any time for "drag" to slow the arrow down. However, down range an arrow with longer vanes (more surface area) or more offset can certainly make a small difference. I don't think you'd see a whole lot out to 30 yards though unless you "overdo it".

The statement about "pure physics" also assumes that both arrows are using the same fletching at the same angle. There are just so many variables in all this stuff.

RE: question about arrow weight and speed loss
 

The exact same thing would happen even if you did shoot the two arrows from the same bow. The lighter arrow would lose a significantly higher percentage if it's speed and energy than the heavy one would.

The lighter arrow is faster. Increase the speed, you increase wind resistance. Air resistance increases in proportion to the square of velocity. The heavy arrow is slower and has less wind resistance. It doesn't have to spend as much of it's energy cutting through the air as the light arrow. PLUS it's additional mass allows it to use even less of it's energy to cut through the air resistance.

As I've often pointed out, if light arrows can't even penetrate AIR as well as heavier ones, how could anyone think they penetrate as well on game? That's another side of the same issue.

Here's something to peek at for a bit of background on archery ballistics.
http://home.att.net/~sajackson/archery_physics.html

RE: question about arrow weight and speed loss
 

tfox, by the time the arrow was in the chrono - the bow is out of the equation - it isn't even a factor is it? how would that fit into the equation? i don't think it does - i think artp is on the money again.
i can tell you i'll be building my 3d arrows a little differently this year.

RE: question about arrow weight and speed loss
 

so are you guys saying a 600 gr. arrow traveling 250 fps has a flatter trajectory than a 415 gr. arrow traveling at 285fps?

RE: question about arrow weight and speed loss
 

Aruthur P - interesting article. You will note that there is no mention of arrow weight as being a factor in the arrow's flight, once it leaves the bow. This is also the case in rifle bullet ballistics. If a 100 grain 6MM bullet has the same ballistic coefficient as a 200 grain .30 caliber bullet, and they have the same muzzle velocity; they will fly the same out to infinity. Central principle of ballistics. Timeof flight is what matters, and that is controlled by the ballistic coefficient of the projectile as well as the initial muzzle velocity.

RE: question about arrow weight and speed loss
 

At distance. It may not be realized until after 40 yards but yes, at 80 you will see a definite difference.

RE: question about arrow weight and speed loss
 

True, except for the fact that you are comparing apples and oranges. Same ballistic coefficient, yes. But you have to reduce the size of bullet to retain that same coefficient. Change that 100 gn bullet into a .30 cal like the 200 gn, and you've changed the sectional density dramatically, which also drastically changes the ballistic coefficient.

Fortunately, our arrows are hollow. That gives us some real opportunities to customize our arrows according to our needs. We can change the sectional density of our arrows to improve their ballistic coefficient by adding weights.

We want to improve long range trajectory, or we need better energy retention for better penetration on larger or tougher game, or to shove a broadhead with a large cutting diameter through? No problem.

So, we slide a weight tube inside the shaft, or use brass or stainless steel inserts, or maybe bump up to a 200 gn point instead of a 100 gn point. Or maybe we do ALL those things. And there it is. We've increased the arrow's sectional density and improved it's ballistic coefficient without altering the arrow's diameter or profile at all.

RE: question about arrow weight and speed loss
 

But bullistic coef is not exactly drag coef, or friction coef. bullistic coef is a matters efficiency to reach a target, and thats where momentum and wieght is a factor.Not just the shape of the bullet.People get bullistic coef and drag confused. Or think they are the same thing, and they are not.

RE: question about arrow weight and speed loss
 

Mark - if you study the various charts/programs used to calculate the trajectory of a bullet, you will find that the weight of the projectile is not really a factor in the equation. Although, generally, heavy bullets have better B.C.'s than light bullets; there are some very long slender bullets in the .22 and 6MM calibers that have B.C.'s comparable to the larger bores - and, in that case, they shoot just as flat - sometimes flatter, since their initial velocity is often higher.

What I hear being argued here, in principle, is that a given diameter arrow would have more drop at close range, but less drop at long range, if you made it heavier by adding some weight to the inside of the shaft. And I'm saying that the initial velocity will go down because it is heavier - and that it will never recover that velocity over distance because the ballisitic coeffcient of the arrow never changed. All that changed is that you had to move the 20 yard pin down a little to compensate for the slower arrow; and subsequently altered the upward arc of the arrow's flight.

RE: question about arrow weight and speed loss
 

Remember,when you increase arrow weight you increase momentum RIGHT,we agree on that therefore you are seeing less loss of energy.


The same thing happens when you increase the energy source,The longer draw or heavier poundage produces more momentum.



If you shoot the lighter arrow out of your bow it will have more momentum than it does out of his bow so there is no way you will experience as much of a loss of speed than when comparing 2 different bows with 2 different arrow weights.


You will see a slightly higher percentage of speed loss from the heavy to the light arrows from the same bow but no where near the percentage loss when comparing 2 different bows with different amounts of stored energy.


Now I can go back and read the rest of the responses.

RE: question about arrow weight and speed loss
 

Tom Crowe a long time 3-d pro shoots ASA with an 80# bow and will setup the heaviest arrow to get 280 fps.


The whole reason is to get as much momentum as possible.That is why he uses 80# and shoots a heavier arrow.


A 60# bow will not yield as much momentum shooting the same 280 fps.Provided they are relatively the same in ibo ratings.

RE: question about arrow weight and speed loss
 

it won't produce as much momentum only because the arrow is lighter.

RE: question about arrow weight and speed loss
 

Exactly, because wieght and momentum is already factored into BC. Not drag coef, or friction coef, but BC only. Maybe we are saying the same thing.

RE: question about arrow weight and speed loss
 

No it won't that is why the light arrow will lose more speed when shot from the same bow but it won't lose as much when shot from your bow as it does when shot from his bow and then compared to your bow with a heavy arrow.


You must compare apples to apples,shoota light arrow from your bow and you will see there isn't nearly as much difference in the 2 arrowswhen shot from the same bow.Especially at 23 yards.

RE: question about arrow weight and speed loss
 

There will be minimal difference in KE but a significant difference in momentum between a light and heavy arrow shot from the same bow! Even though the difference in KE will only be a couple of Ft Lbs, a 700 grain arrow will have approximately 30% more momentum than a 350 grain arrow when shot from the same bow.

edit: LOL! Shouldn't go messing around with all this arithmetic and stuff before my 2nd cup of coffee. Had to make a correction...[8D]

Interesting note though... Say the bow you're shooting spits out your arrows with 70 ft lbs of energy. You decide you want to try and get the 350 gn arrow's momentum to match the momentum of that 700 gn arrow. You have to drive that 350 grain arrow to 430 fps and 143 ft lbs of energy to get there.

RE: question about arrow weight and speed loss
 

Mark - you know I thought about this last night, while sipping on a glass of very old Scottish whiskey. Started playing the devil's advocate against my own logic . . . . .

Suppose is I go out to my lathe and produce a rifle bullet made out of aluminum - to the exact shape and diameter of a .30 caliber 220 grain Sierra Matchking. Let's say it only weighs 125 grains. And I also produce an identical shaped bullet out of machineable tungsten - and this bullet weighs 290 grains. Both bullets have exactly the same ballistic coefficient, right? If they were launched at exactly the same velocity, I can't see any way the aluminum bullet is going to fly as far as the tungsten bullet. Kinda like steel shot opposed to lead shot. But if I plug the numbers into my Exbal or Infinity program, they come out the same. Now I'm kinda confused . . . .

RE: question about arrow weight and speed loss
 

Roskoe,

In your example of the tungsten versus aluminum bullet, they'll have the exact same shape, as you cited, but they won't have the same ballistic coefficient.

The reason is because the ballistic coefficient of a bullet is dictated by the bullet's sectional density, and the sectional density is the ratio of the bullet's diameter to its weight.

So the tungsten bullet will have the identical shape as the aluminum bullet, but will have a higher ballistic coefficient due to the higher sectional density.

RE: question about arrow weight and speed loss
 

Arthur,do you not agree that a 370 grain arrow has more momentum shot at 260 fps than it does when shot at 230 fps.Therefore it will retain more speed downrange than the 370 grain arrow shot at 230 fps.


This means the 260 fps arrow willlose less speed at 20 yards than the one that is shot at 230 fps.


I agree with the momentum being the reason for a difference but you still aren't comparing apples to apples.


1 more thing,I can change the speed of my arrows just by shooting through a different spot in the chrony,up to 4 fps if I remember correctly but my chrono bit the dust so I can't say for sure.

RE: question about arrow weight and speed loss
 

Nope, they will have totally differnt BC's but the same drag coef. Two diffferne things. One has much more momentum than the other.

RE: question about arrow weight and speed loss
 

Heavier objects have more momentum, thus they are harder to slow down.

Example: Go outside and throw a baseball as hard as you can. Then throw a wiffle ball as hard as you can. See which one slows down quicker. The heavy one or the light one.

RE: question about arrow weight and speed loss
 

Did you read any of the replies? That has been stated,just more to it in this discussion,actually,these discussions.;)

RE: question about arrow weight and speed loss
 

True, the 370 gn arrow at 260 fps will have more slightly momentum. However, it will lose a greater percentage of it's speed, even at 20 yards, than the same arrow at 230 fps. You increased the speed BUT, wind resistance (drag) increases by the square of velocity.

The 260 fps arrow will still arrive at the target with more energy than the 230 fps arrow had at the bow. The ballistics table shows the 230 gn arrow starting out at 230 fps, 43 ft lbs of energy and arriving at 20 yards doing 219 fps and 39 ft lbs. The 260 fps arrow: 260 fps, 55 ft lbs and 248 fps with 51 ft lbs at 20 yards.

That's a loss of 11 fps and 4 ft lbs for the 230 fps arrow. 12 fps and 4 ft lbs for the 260 fps arrow. The differential in energy loss between the two arrows is too slight to be worth considering at 20 yards but it is measurable... if you want to run the calculator out to that many decimal places. ;)

Contrast: I ran a 570 grain arrow at 185 fps to match the energy of the 370 gn arrow at 230 fps and checked the numbers at 40 yards. Starting at 185 fps with 43 ft lbs, it hits the 40 yard target at 175 fps and 39 ft lbs.

That arrow lost 10 fps and 4 ft lbs. It yields roughly the same numbers at 40 yards as the 370 gn arrow put up at 20 yards. That's why it's better to get your momentum from mass than from speed.

(By the way, that 570 gn arrow at 185 fps is almost exactly the arrow I use and speed I get from my recurve.)

Just for grins, the 40 yard numbers for the 370 gn arrow: 230 fps is down to 209 fps, from 43 ft lbs to 36. Loss of 21 fps and 7 ft lbs. 260 fps arrow is down to 236 fps, 55 ft lbs is down to 46. Loss of 24 fps and 9 ft lbs. The 260 still arrives at target with more KE than the 230 fps started out with but it still lost a higher percentage of it's speed and energy.

RE: question about arrow weight and speed loss
 

For me to get as much difference as they had I would have to increase another 100 gr of arrow weight on my bow.Even then at 20 yards I would only be 6 fps difference in the amount of speed lost.


That is comparing 657 gr arrow to a 367 grain arrow.I lost 7 fps with the heavy arrow and 13 fps with the light arrow.This was using my ballistic program.

I can't get into it now because of a computer glitch but this was some info I had saved.


I still believe he needs to test it to see if he would lose as much when shot from the same bow.My program shows is does not.Atleast I think all the info was the same on the 2 sheets I had saved.