I was practicing shooting today and two of my shots went a little farther forward than i would have liked. This lead me to start questioning if I have enough KE to penetrate a deer's shoulder and still have a lethal shot. I am using Carbon Express Predator II arrows that weigh 431gr including a 100gr tip. They are being flung from a 2010 Bear Strike with a 30" draw and 70# weight. Yea i know the arrows are a little short but they are over an inch from the front of my rest. How much KE do i have (if any of you know how to figure this out) and how much would it take for an ethical shot through a shoulder in case buck fever gets the best of me in the season?
I reply with enough for you to figure it out hopefully. Kinetic Energy can be found using the following formula: mv^2/2 or half the quantity, mass times velocity squared. The mass of your arrow and tip are 531 grains. The velocity (distance over time) of your arrow is simple since you are at 30" and using 70lbs because that lines up with the IBO speeds listed on bear's site of 310 feet per second. Plug those values into the formula above and you'll have the kinetic energy for your bow, although it will be in foot grains per second squared. So you'll have to do some conversion to figure out what that means in a realistic sense.
MHS. You have nothing to worry about...30 inch draw + 70 lb draw weight + 431 grain arrow=death. Here are the Carbon Express Predator II specs: 2040 -598 spine Max length 30" B.O.P - 7.7 GPI, Nocks and Inserts included. 3050 - 505 spine Max length 30" B.O.P. - 8.3 GPI, Nocks and Inserts included If you are using either one of those arrows your spine is too weak more than likely AND you more than likely do not have a 431 grain total arrow weight unless you are using some weights up front.
I agree, If you hit a deer with that set up, it will die!!! Only thing you need to worry about, is hitting the kill zone. If you do, I believe it will be a pass through.
As others have already told you, yes you have more than enough KE for a decent or even marginal shot. For a bad shot, no amount of KE will help. Put it in the boiler room and you'll be fine.
You'll see a lot of people moving away from KE and towards momentum. I don't disagree with line of thought. However, you have to be logical. The way the equations are derived, you gain ke through speed and you gain momentum from weight. Its all a tradeoff and you have to find what works for you. If your arrows are in fact .500 spine, they're pretty weak and if you can, move to a 340 or 350. Also, arrow length is a preference. My local shop says an inch more than draw. My arrow and draw length are the same. A guy I work with is 3/4 of an inch less than draw. It depends on your setup. My setup is 377 grains and is at 290 fps. I believe that is a very ideal place for both ke and momentum.
I will try to lend some help here, but i am no expert by any means, i have been researching about arrow selection, because im worried my girlfriends bow wont have enough penetration. i have read several articles saying, for a heavy arrow (use for elk, or moose) go with 8 to 10 grains per pound of draw weight. for a medium arrow (whitetail) 6 to 8 grains per pound of draw. for a really light arrow (short shots, target, etc) 5-6 grains per pound. and i believe you should never go less that 5 grains per pound. or else it is not very safe. hope this helps some,
Virginia, I am shooting the 60/75 Predator II which with my draw length and weight is spined properly for my bow (trust me its shooting prettier than any setup i have had previous). I am confident of being able to put my shot in the kill zone i was just worried about being able to make it through bone (either shoulder blade or rib) with enough energy left to ensure a good clean kill.
MHS, then my first statement stands... "MHS. You have nothing to worry about...30 inch draw + 70 lb draw weight + 431 grain arrow=death." You have as good a chance as anyone to soften a marginal hit.
I'm not gonna tell you that you have this much KE and you need this much. I'm going to tell you that you'll have enough KE to shoot anything you want up to large game. No worries!
I did the math, your kinetic energy is over 110 ft-lbs. Which if you look at this link Easton Kinetic Energy Chart, you'll find you're more than okay.
