Does a higher kinetic energy open up more shots for a bow?

[h5c5o5]

Hello everyone
In a pre elk hunting delirium I have been looking at new bow setups that maximize the kinetic energy (KE) of your arrow. I was busy laughing in a insane mad scientist manner when I stopped to ask myself if more KE was really going to change anything. I am shooting at 81 ft/lbs at the moment and was crafting theoretical bows that would pack 120+ ft/lbs wallops.

I guess my question would be, are there any shots you could take with a 120 ft/lbs bow that you wouldnt be able to take with an 80 ft/lbs bow (if we are talking about elk)? Will that force allow you to blow through shoulders now? Will it shear rib cages in two? Will it shift the killing potential of a bow more towards shock and trauma (like that of a rifle) or are we just talking bigger bleeding holes? What are your guys thoughts on the matter.

Cheers
Henry

[sebek556]

In my opinion, it would help in the rib cage, not for the shoulders. No current set up will put archery into the shock trauma category. It is still and I think will be a long time a bleed out shot. Don't try to get fancy with your shots. fancy ends up with wounded game, and a bad name for hunters.

[Button Nubbs]

80 ft/lbs is quite a bit I personally wouldn't take a shot with a 100lb bow that I wouldn't take with my 60lb bow. "Kinetic energy" is somewhat misleading imo. Momentum is what drives the arrow home. I think in general we as archers tend to get caught up in over thinking things like this. Shoot something that is comfortable and accurate for you.

[h5c5o5]

Oh I definitely agree with you fellas that with a modern compound bow (or any bow for that matter) the most important part of the equation is the judgement and aim of the archer. I guess I was wondering, on a broader note, if you all thought that the bows of the future (say 2030) were going to be noticeably better than bows now. They might be a bit faster and perhaps a tad lighter; but are they going to offer any real advantage or will archers still be taking only broadsides or quartering away shots at 50 yrds or under.

[Smokey Bear]

Momentum and KE are closely related.  They are both products of weight (mass) multiplied by speed (velocity).  That aside, I have seen a very standard bow set up, at 30 yards, blow through one side of a rib cage, slicing through a rib on the exit.  I don't know how many foot/lbs that arrow was packing but it wasn't anything extraordinary.  Also I have seen several shoulder shots with the broadhead and/or arrow bent.  I don't think the arrow can hold up to a lot more Energy and stay intact???

[Button Nubbs]

Good point about the arrow holding together. I wouldn't have thought about that. I'd hate to be spitting out pieces of carbon from my elk steak.

Kind of crazy to think that if these bows get a whole lot faster we might start seeing .150 .100 or who knows even .050 spine arrows.

[jechicdr]

I suspect penetration is the most important factor.  An arrow with a lot of kinetic energy will lose energy as it passes through and animal, but is likely to have enough energy to keep on going further than an arrow with less energy for the most part.

But imagine a diver slicing through the water from a 10 meter diving board and then imagine one diving from 3 thousand feet.  The higher elevation diver will have much more kinetic energy but will likely shatter on impact and create a huge splash but penetration will likely not be that impressive, though will still probably be more than the 10 meter.

Next imagine a 10 lb knife (Now that's a knife) dropped into a pool of jello and then dropping a 10 lb ball into same pool.  They will have nearly the same kinetic energy but the knife will penetrate a lot further while the ball will likely just "make it jiggle"

Hitting a shoulder with a high energy arrow can destroy your head and stop the penetration or shatter the shoulder...which will require energy which has to come from the arrow, where a lower energy arrow may retain the blade and slice the bone and still result in improved penetration because once through the shoulder, it still has a cutting surface.  The second scenario would be more the difference between a cut on contact versus a trochar tip.  The one benefit to the trochar tip is that it may shatter the bone, so the bone doesn't shatter the blades.

[whacker1]

There is a good thread on Archery Talk, which discusses the optimum arrow weight to maximize penetration.  Too heavy and the arrow doesn't get enough speed to optimize penetration.  Too light and while you have the speed, you don't carry enough momentum and kinetic energy to maximize penetration.

The results were to be in the 6.5 to 6.7 grains per pound of draw weight.
ElkNut was the one performing the test.  I will post the thread later when I find it again.

So rather than focussing on draw weight, speed, and technology, make sure you have the appropriate combination of equipment to maximize penetration with your current set up.

You still shouldn't be shooting at shoulders, but hopefully with an errant shot, you will get the maximum opportunity for taking down the animal

http://www.archerytalk.com/vb/showthread.php?t=1731614

[et1702]

Yes and no.  How's that for an answer?  FYI, Momentum is better than KE.  To get more momentum, you need heavier total arrow weight.  The more momentum your shaft has, the less energy it will loose as it passes through an object (assuming the weight stays constant).  Lots of good info on this site regarding KE, momentum and arrow penetration:  http://www.alaskabowhunting.com/Ashby-On-Momentum-Kinetic-Energy-Arrow-Penetration-W19.aspx

Since momentum is Mass X Velocity, one of the things you can do on-line for some theoretical testing is play with the on-line KE calculators.  You will notice that for a specific weight bow (say 70lbs), IBO speed of you bow, draw length, etc. all being constants, and you change the weight (i.e., Mass) of the arrow, that you will see KE go up to a certain Maximum point and then start to drop off (i.e., get less).  This is because velocity starts to drop faster as you add more weight, but momentum will not drop off.  It will actually still be increasing as you increase arrow weight.  But, not many people want to shoot a 750gr arrow.  So, I typically find the point where KE starts to drop off and shoot shafts within this range, which gives me max KE, max Momentum and still relatively flat shooting arrow.  With my particular bow (set at 70lbs), I have found this point (i.e., range of max KE) to be between 500gr and 550gr total arrow weight.  Depending on which shafts I shoot, my arrows are either 525gr or 540gr using a 150gr BH (to increase FOC). 

So, in other words, the bow you shoot has a limit to max KE & momentum (at a particular weight that is comfortable to shoot).  Find that limit and that's the Max penetration you can expect.  If you look at two arrows with the same momentum, one a heavier shaft at slower velocity compared to a lighter shaft at higher velocity, the laws of Physics require that the heavier shaft will out penetrate the lighter shaft.  FYI, the arrow with greater FOC will also typically out penetrate, with all else being equal.

But, I still wouldn't take a shoulder shot on purpose.  Broadside or quartering away only!  Elk are tough.  Maximizing momentum and shooting a really tough BH might help if your shot is off the mark.  However, out of respect for the animals, I'm not willing to test.

ET

[colockumelk]

That penetration test that elknut did was AWESOME!!!!  I learned ALOT!! I had always assumed that heavier was ALWAYS better and that higher momentum was better.  Especially at longer ranges.  But his test showed that the best penetration range for weight was 6.5-6.7 grains per pound of draw weight. Also FOC had A LOT to do with penetration such as two arrows that weighed the same amount for instance, the one with 16% FOC way out penetrated the one (remember same overall weight) but had like 12% FOC.  I knew FOC helped in penetration but didn't realize how much it made a difference. I recommend reading through it all.  AWESOME test.

[Tealer]

So does actual bow speed, or draw length come in to play? I am shooting FMJ 12.0gpi and a 125g tip. But I'm at 31 1/2 draw length and 70 pounds. But I'm still at 7.18.