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.