Optimal ke/trajectory question
 

I was playing around with the speed/ke calculating spreadsheet that I made a while back plugging in different arrow weights and such and as far as ke is concerned, at my draw weight/accessories/etc... 440 grains seems to be the optimal arrow weight for my setup. By that I mean when I go over 445 grains, my ke starts to drop. Does this mean my bow is most effecient with a 440 grain arrow and it is actually hurting me to go to a heavier arrow? At what point does it become fruitless to shoot a heavier arrow at the expense of ke & trajectory?

Coincedentially, my ACC 3-60s with feathers and a lighted nock with 100 grain broadheads weigh in at 442 grains and shoot 287 fps with almost 81# of KE.

RE: Optimal ke/trajectory question
 

I kind of don't pay attention to KE. On the 3D course speed is what counts not energy. While hunting momentum counts and not KE. Momentum and KE will have a max and i would have to say that you found your max. What it really does for you i don't really know maybe someone can explain why KE matters.

RE: Optimal ke/trajectory question
 

I thought there was a website somewhere that would show your momentum in relation to ke. I had thought is was BowJackson's website but I didn't see it there.

RE: Optimal ke/trajectory question
 

All that i know is momentum is what determines penetration. Not KE.

RE: Optimal ke/trajectory question
 

KE is the mass of the arrow times the velocity squared, this causes kinetic energy to depend more on the speed for a higher value.
Momentum, on the other hand is the mass times the velocity. Momentum is how difficult it is to stop the arrow, the higher the momentum, the better penetration.
Inertia is what makes an object difficult to stop. Inertia is how much an objects resists acceleration in either the positive or negative direction by an outside force, such as the friction of piercing an animal. Momentum is derived from this. It is proportional to both mass and velocity. Kinetic energy is not directed in any way, it is just a number, while momentum is a vector, meaning it has both magnitude and direction. I hope this helps.

RE: Optimal ke/trajectory question
 

It is a difficult concept to understand and I tried to simplify it as much as I could and tried to avoid the details. I have taken a few years of physics and different kinds of calculus in my short life and I still have to pause and think about the difference before I write it out. Both are important when talking about an arrow, but momentum is what you use to figure out the penetration because it is a vector and is directed into the animal's side, while the friction is working against it by pointing out the animal's side along the same axis as the arrow. The net force resulting from combining these vectors is what determines penetration (how long it takes for the velocity of the arrow to reach zero).

RE: Optimal ke/trajectory question
 

It is a difficult concept to understand and I tried to simplify it as much as I could and tried to avoid the details. I have taken a few years of physics and different kinds of calculus in my short life and I still have to pause and think about the difference before I write it out. Both are important when talking about an arrow, but momentum is what you use to figure out the penetration because it is a vector and is directed into the animal's side, while the friction is working against it by pointing out the animal's side along the same axis as the arrow. The net force resulting from combining these vectors is what determines penetration (how long it takes for the velocity of the arrow to reach zero).

RE: Optimal ke/trajectory question
 

DO you know the formula for figuring momentum? If the first part of the calculation is M x V what is the divisor?

RE: Optimal ke/trajectory question
 

Mike.

There is all that on Bow Jacksons site

RE: Optimal ke/trajectory question
 

your speed and k.e. is far greater than any animal on this planet can handle at any accurate shooting yardage!!! how do you think the indians killed moose ,elk,bear? not with a bowtech or a mathews!!!! only with sharp arrow heads,shot placement and skill to get inside a comfortable kill zone..get back to the KISS method and you'll be more successful in your hunts. technology is an advantage, not a mandatory factor. if you shoot a 350 grain arrow in the kill zone at 30 yards and a 550 grain arrow in the same spot at the same yards, both will get a clean pass through. only at longer ranges does heavy arrows with greater speed + more k.e. = any more advantage..i've got 2 velocity specialists in my family..don't get caught up in the marketing hype. shoot accurate at your comfortable range and hunt within that distance. isn't that what bowhunting is all about, getting close to you prey???

RE: Optimal ke/trajectory question
 

What else do we have to do in the off season?:(

Seriously, that is is very good point and one that need to be remembered.

RE: Optimal ke/trajectory question
 

jca,I do agree with most of your post but not all heavy arrows retain more speed or ke than the lighter counterpart.An ACC and a Kinetic II will retain more of it's original velocity and ke downrange than an aluminum arrow.Also a heavy arrow will generally require more guidance at the backend of an arrow to get a heavy arrow to fly accurate at longer distances than it will a lighter arrow and therefore,more fletching equals more drag.ACC's are some of the best penetrating shafts on the market but are substantially lighter so the arrow make up plays a huge part in the equation and isn't just weight,verses speed, verses ke, verses ke.



By definition,ke will play a huge role in penetration but so does momentum.Ke is part of what helps keep an arrow straight in flight and that is a big part of penetration,more ke equalls more inherant ability to remain traveling straight and PARALLEL on impact.Momentum gives you more bone crushing force to basically just keep going regardless of what gets in it's way and speed gives you friction fighting ability so basically just get a well balanced arrow that is well tuned and go hunt and don't overthink this penetration stuff.Shot placement will take care of it.

RE: Optimal ke/trajectory question
 

I think that you may have just figured out the optimal point weight for the spine of that arrow out of your setup rather than the optimal weight arrow for your setup.

RE: Optimal ke/trajectory question
 

What makes you say that?

RE: Optimal ke/trajectory question
 

I think that what you've mostly found is the point weight at which the spine of that particular acc is weakened so that it doesn't retain as much energy. Seems like the 100 grain head is as heavy as you can go for that arrow. And that's good lots of broadhead offerings in 100 grains. But I do wonder for instance if you went to a heavier arrow like a big game 100+ if you wouldn't find that the KE would be retained at a heavier arrow weight given the heavier spine. Or maybe a 3-71 with a 125 point head.

I think the only issue would be is how critical is the bow is at 287. But that is a nice weight to be getting that kind of speed.

RE: Optimal ke/trajectory question
 

I'm still not understanding where you are coming from about the point weight in relation to spine and what effect is has on ke/momentum. As I understand it, KE and to a point, momentum are directly related to speed and arrow weight. I just plugged in different arrow weight for my setup and it automatically caluculates the speed based off the IBO speed I plugged in from my bow. I have chrono'd this bow at IBO specs and it will shoot 326 fps with a tied on nock and bare string. I basically plug that in, deduct for each grain over IBO minimum plus all string accessories and come up with a speed and KE figure. Regardless of what arrow I am using for the weight calculations, I don't see how your scenario has any bearing on the ke or momntum. Simply put, it reaches a point to where the lines of speed and KE cross at some point and then both figures begin to go down. On my bow, that optimal combination seems to be 440-444 grains. At 445 grains and above, the KE as well as the speed begins to drop off.


BTW, you were wondering how my bow shoots at 287 fps, here's a pic of a combination 20 and 30 yard group I shot while shooting one pin to get the idea of how the trajectory is on this bow. This was a 390 grain arrow at 308 fps.

RE: Optimal ke/trajectory question
 

Looks like to me that your speed, K.E and accuracy is good enough for anything from sparrows to grizz;) Try some of my favorite XX78 2315's for accuracy and quiet hunting, should weigh around 555 grains in 30 inches and speed will still be around 265 fps.

RE: Optimal ke/trajectory question
 

Nah, these ACCs have served me well over the years. I think I'll stick with them and keep the extra speed. :)

RE: Optimal ke/trajectory question
 

Damn nice group!!! You shooting one pin for hunting?

RE: Optimal ke/trajectory question
 

I stopped after reading this one line......;)

Personally, I am surprised that your maximum KE numbers came out with a 442 grain arrow. In most of the cases I have run through, hypothetically, the arrow weight was significantly higher. However, if you are also factoring in trajectory then I can see where an arrow weighing between 400-450 grains would be the "best of both worlds" for most setups today.

RE: Optimal ke/trajectory question
 

Mike we are shooting almost identical setups, as far as weight and speed, also we are shooting the same bow and draw length. I am shooting 3-71 ACCs and my arrow weight is 444 gr. I haven't done any tinkering with different arrow weights but it did seem like that particular weight and speed combo was going to be the best of both worlds.

RE: Optimal ke/trajectory question
 

Mike, I'm not sure if you are saying you were holding the pin on the same spot, or not, but an arrow going 310 fps will drop from 5 to 6 inches, between 20 and 30 yards distance. This amount of drop will remain virtually the same, regardless of the arrow weight. The trajectory at close range is the same for all arrows traveling 308 fps. The only slight differences occurs at longer distances, when variations in drag and K.E., cause one arrow to slow quicker then another.

RE: Optimal ke/trajectory question
 

Yep, I've only shot one pin for hunting for years.


As best I could tell with a .029 pin at 30 yards on a circle that small, I was holding on the same spot. I guess since the circle was basically covered by the pin, it's feasible to say there may have been some variance (holdover) involved, but I wasn't obviously holding over 5-6" though.

RE: Optimal ke/trajectory question
 

I'm not sure if you are saying you were holding the pin on the same spot, or not, but an arrow going 310 fps will drop from 5 to 6 inches, between 20 and 30 yards distance. This amount of drop will remain virtually the same, regardless of the arrow weight. The trajectory at close range is the same for all arrows traveling 308 fps. The only slight differences occurs at longer distances, when variations in drag and K.E., cause one arrow to slow quicker then another.


WITH ALL THAT SAID DO YOU GUYS THINK THAT MY TERMINATOR 60-75'S WEIGHING 426 WILL SHOOT THE SAME AT 20 AND 30 AS MY CX 300'S WEIGHING 360. I'M DRAWING 62 LBS. 28 IN. DRAW WITH 27 IN. ARROWS.

RE: Optimal ke/trajectory question
 

Shoot the same in terms of point of impact? Accuracy? or Consistancy?

I think that there will be a drop in inches when comparing the two arrow weights you mentioned. Another inch or two at least.