enough kenetic energy
 

hi i have a bowtech liberty and im pulling 70 pounds and im only getting 220 fps. My question is i shoot 2219 and total weight being 525 grains. The kenetic energy is 55 pounds, do u think this is enough to kill a deer out to 40 yards or get a lighter arrow. What do u think i should do? Im scared about not penetrating this fall. Thanks

RE: enough kenetic energy
 

I don't think you'll have penetration issues, but a lighter arrow may help in case your distance judging is off some. Your bow is going to produce about the same KE for any arrow setup you choose.

RE: enough kenetic energy
 

sorry rybohunter, il have to disagree wit ya on that one, that is not true

RE: enough kenetic energy
 

Care to elaborate on that one?

While shooting a lighter arrow he may not get the same ammount of KE, he will however be able to make up for yardage judging problems. The faster your bow shoots the less likely you are to miss if you misjudge the yardage by 2 or 3 yards.

RE: enough kenetic energy
 

I think this is where Rybohunter missed the boat. A bow will not produce the same KE for any arrow set up.

I came up with 56 ft lbs of KE on Jackson's, but whose counting! :eek: Having said that, it is plenty for white tailed deer. If I was going after Elk, moose, bear, etc, I would want a little more KE. Just make sure you are using a good fixed blade broadhead. I would steer away from mechanicals. How long is your draw length? Do you use rubber tubing on your peep? What is your string loaded down with? Are your limbs bottomed out? These are things that can be addressed to maybe give you a little more umphhh!!! If it were me, I would lighten that arrow up somewhat as well. Good Luck!

RE: enough kenetic energy
 

I hate to burst some bubbles here, but rybohunter is right on this one, at least normal hunting distances (30 yds). If you don't believe it, get an archery program like The Archery Program (TAP), and compare the KE that your favorite bow will put out with different weight arrows. From 0 - 30 yds, the KE will darn near the same, no matter what weight arrow you use. Even at 50 yards, the difference between a 320 grain and a 520 grain arrow will be at most 3 ft lbs of KE with a 300 - 305 IBO rated bow.

RE: enough kenetic energy
 

All I have to do is take my chrono and shoot my bow with several different weights of arrows and record the speeds. My bow produces within 1-2 # of KE regardless of arrow setup. A stiffer arrow seems to transfer the energy a little better which is where I think the small variations come from.

RE: enough kenetic energy
 

Iwould be very hesitant about using mechanicals at that distance though.;)IMHO

RE: enough kenetic energy
 

If we assume 100 grains of virtual mass (thats pretty typical) then a bow that launches a 525 grain arrow at 220ft/sec (which is 56.4 ft/lbs KE) will launch a 350 grain arrow at precisely 259.3 ft/sec which is 52.3 ft/lbs of KE. Thats a 7.4% drop in energy launched. This difference will increase slightly at longer distances due to the fact that the heavier arrow because of slightly greater momentum will maintain slightly more of its energy.

If bows transferred 100% of their stored energy to the arrow then it wouldn't make any difference what weight arrow you used as far as energy launced goes but the reality is that they are not 100%. It depends on the bow of course but values of around 83/84% efficient are typical for launching 500 to 600 grain arrows and values around 75/76% are typical for launching 300 grain arrows. The lighter the arrow the less efficient and therfore the less KE.

A good way to explain the efficiency change is to think of throwing a ping pong ball verses a golf ball against a window. They are roughly the same size but because the golf ball is heavier you can transfer more energy from your arm to the golf ball. Don't try it but I bet you can break the window with the golf ball but I doubt you could with the ping pong ball.

RE: enough kenetic energy
 

I killed a big Kansas buck with 27 pounds of KE at 18 steps, arrow passed through both sides.

RE: enough kenetic energy
 

gru, you have a heavy arrow, but an extremely good one for hunting. Your set up will blow through all medium and big game and more than enought kinetic enegry if you decide to hunt elk size game. If your interested in 3-D shooting you may want to choose a lighter aluminum arrow.;)

RE: enough kenetic energy
 

Olink, I have no idea what program your using, but if that software is telling you that a 550 grain arrow at 255 is going to deliver the same kinetic energy as a 400 grain arrow at 280, their are blowing smoke up your butt. Take your baseball and throw it against your garage door than borrow your wife's bowling ball and throw that at the same door. Now tell me which one has more kinetic energy. The fast baseball with little weight or the slower bowling ball with 10 times the weight. Same same when throwing a javaline, shooting a bow or your favorite bullet.

RE: enough kenetic energy
 

40 yards is a long ways in actual hunting conditions. 30 yards your set-upis fine. But 40...unless your a fanatical great shot......the deer is broadside......looking away.....standing still......with no wind......and you got your range finder on it....pass. There's way to opportunities inside 25 that are almost automatic. You can practice 3D all day at 40..50 and 60 and pipe the kill zone....but on a live deer at 40 its another story.

Good Luck!

RE: enough kenetic energy
 

Sniper, I don't know whose post you were reading, but it sure wasn't mine. I didn't use any of the numbers you stated in your post. The Archery Program is a VERY well respected estimation tool, and I challenge you to find anyone who has found errors in its calculations.

RE: enough kenetic energy
 

i did that thing is junk

RE: enough kenetic energy
 

Sniper, where did you get those numbers from? I don't remember seeing any of them in this thread.

Did you you guys read the post by datamax? It's true. I know for a fact that ton's of KE are not necessary for deer. In fact 24lb/ft is adequaite if the person shooting the bow does his part. This KE arguement does really get pretty old and shows where the amateurs are. Prett much, I figure that any person who has to ask this question has more than enough with their setup. OR do they think they need more "power" to compensate for their shooting ability?

RE: enough kenetic energy
 

If I was going to throw both of them at you as hard as I could, which one would you rather get hit with? The bowling ball because I only have X amount of energy with which to throw a blowling ball and while it my have more KE, I can't get enough speed from it to hurt you. With the baseball on the other hand I will be breaking some bones if I hit you with it. Those two comparison aren't really valid here considering the extreme differences in weight. All that being said you won't see more than 1-2 foot pounds of difference when going from say a 300 gr. arrow to a 500 grain arrow. Also, there is something called the law of deminishing returns. In other words a cam may more more efficient up to a certain weight and any extra arrow weight you add after that point will actually decrease efficiency.

RE: enough kenetic energy
 

How about if we rolled them? [8D]

RE: enough kenetic energy
 

Talk to compound shooters and they think they need 70 pound bows shooting 300 grain arrows so they can get a KE calculator to tell them they have 60 pounds or some arbitrary number and its almost laughable.

Talk to any trad shooter who shoots 650 grain wood arrows from 50-55# bows with speeds at maybe 170-180 fps and ask them about KE.

Truth is a sharp broadhead on the end of an arrow will kill ........ ya'll are arguing about how many inches you'll stick the arrow into the dirt on the other side.

This ............ from a 52# longbow, 525 grain carbons, a Thunderhead 3 blade and the shot was 18 yards.

RE: enough kenetic energy
 

silentassassin wrote: A bow with 100 grains virtual mass throwing a 300 grain arrow 280 ft/sec WILL throw a 500 grain arrow at precisely 228.6 ft/sec. In terms of KE thats 52.2 ft/lbs vs. 58.0 ft/lbs respectively or a 5.8 ft/lb increase. In terms of efficiency the bow transfers 75.0% of its energy to the lighter arrow and 83.3% to the heavier. This is not opinion its is mathmatical certainty. You are simply incorrect when you say you won't see more than 1-2 ft pounds of difference. Also, with regard to a point of diminishing returns in efficiency, efficiency always increases with arrow mass at least over a practical range of arrow weights.

Although I disagree with your numbers I do agree with the point you are making. The difference between 50 ft/lbs and 60 ft/lbs is, as datamax said, how deep the arrow goes into the dirt after passing through the deer.

RE: enough kenetic energy
 

50 ft-lbs of kinetic energy should be more than enough to harvest about any animal in north america.

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RE: enough kenetic energy
 

I'm not sure about other folks here but unless the person throwing the baseball and bowling ball is the size of the Olsen twins , I'd rather get hit by the baseball!:eek:

Second thought , I dont care how big you are , I'll take the baseball!