Kinetic Energy

[darwal44]

Hi, I am Dennis from Peru. Does someone knows what is the kinetic energy of the Buldog 400 model?

Thanks

[paulaboutform]

Hello Dennis. The kinetic energy is determined by the weight and velocity of the projectile. Here's the formula.

Weight × Velocity × Velocity ÷ 450240 = ft/lbs K.E.

Paul

[darwal44]

Thank you Paul. You mean weight in grams? And velocity in foot per seconds?

[paulaboutform]

Hello Dennis. The kinetic energy is determined by the weight and velocity of the projectile. Here's the formula.

Arrow weight × Velocity × Velocity ÷ 450240 = ft/lbs K.E.

If a BD400 is shooting a 350gr arrow at 400fps then

350 × 400 × 400 ÷ 450240 = KE

Paul

....the arrow weight is measured in grains...same as bullets. Velocity is feet per second.

[darwal44]

I understand. Thank you Paul.

[hunter with MS]

it is arrow speed X arrow speed X total arrow wt. Divided by 450240.

[darwal44]

A friend of mine did the calculations.

http://www.mediafire.com/view/tq6it508trj9pd1/Cinetica.JPG/file

[SEW]

Here’s something that might help.This was something I did about a year ago. I have 2 405s, a BD400 and a M380.
My BD400 is shooting about 10’/sec slower than my M405. So subtract a little. This was with a 20” Zombie with a total wt of 418.6g.

20" ST 418.6g M405
1yd 369'/sec . 127ft-lbs.
20yd 360'/sec 120.
40yd 354'/sec 117.
60yd 337'/sec 106.
80yd 325'/sec 98.
100yd 311'/sec 90.
So from 20 yards to 100 yards only 58'/sec (16%) was lost while only 30ft-lbs (25% )of the energy was lost. More energy was lost due to the speed squared factor of the formula E= MC(2). Any energy above the minimum required (34'-pds) or desired (40'-lbs) for deer (20 more for bear), for moose, elk 55’lbs and more is just gravy. These energy levels are for "average" fixed blade broadheads. Its been stated, correctly so in my opinion that once adequate energy has been reached, trying to get more energy by sacrificing speed is not desirable. I agree totally. With this in mind, the energy loss of 25% from 20-100 yards is irrelevant since still over twice the energy needed still remains.
So, what can we derive from this? First off, my heavily noise/vibration attenuated M405 has been slowed to where it is just upper mid level, performance wise. These shots were all made with a 5-8 mph l-r xwind. The accuracy of the M405/20", 92g insert, 125 Griz Trick, helical Blazers, flat plastic nocks is incredible. Since the M405 is actually sighted in with Lumenoks , I aimed off slightly to help preserve my chronograph . Still, in spite of the wind and the 20g difference in nock weight, I felt comfortable testing out this far. No target practice has been done with this Xbow since mid-September. Its only shots were deer kills. It's still on.
Back to the results. Contrary to what many have stated, energy loss seems to be a non-factor even out to 100 yards. Trajectory, range estimation error, and time of flight remain the critical and limiting factors. O.88 sec to 100 yds, 0.51 sec to 60 yds.

Why all this? Because of repeated comments on various forums concerning loss of energy at what many consider "extended" ranges (40-60 yards). I've been repeatedly chastised for shooting at these ranges because "not enough energy" remains for an ethical kill. False!! However, some broadheads can require a tremendous amount of energy to get a passthru (FOCs). After all my promotion of FOCs for higher powered xbows, I've now discontinued their usage in favor of (currently -verdict not in) Grizz Tricks. I want passthru's . I killed a 100#+ doe p(though the picture doesn't look like it's that large) last Fri with a GT(2nd deer of year with this BH). Massive blood trails.

[darwal44]

Wow! You realy have been experimenting with your crossbow. I agree that it is velocity the most importante factor, because you do not need a great amount of energy to kill deer or bear.
Thank you Sew foe sharing the result of your experiments.

[nchunterkw]

SEW makes some good points, but not everyone agrees that KE is the be all end all. I for one look at the momentum of the arrow and not the KE. Arrows kill by going through the animal making penetration the second most important factor for a killing shot next to shot location. Momentum is velocity X weight. Two arrows can have the same momentum, but one derive it more from arrow speed, while the other derives it more from arrow weight. The heavier arrow will penetrate further every time. If interested, you may want to look at some papers written by Dr. Ed Ashby on the subject. Here is a good link
http://www.grizzlystik.com/Ashby-On-Momentum-Kinetic-Energy-Arrow-Penetration-W19.aspx

Killing deer is not so hard as our equipment has lots of power, but as you can see in my avatar I also hunt larger game with my crossbow and that has driven my position on arrow momentum.


Good Luck!

[SEW]

SEW makes some good points, but not everyone agrees that KE is the be all end all. I for one look at the momentum of the arrow and not the KE. Arrows kill by going through the animal making penetration the second most important factor for a killing shot next to shot location. Momentum is velocity X weight. Two arrows can have the same momentum, but one derive it more from arrow speed, while the other derives it more from arrow weight. The heavier arrow will penetrate further every time. If interested, you may want to look at some papers written by Dr. Ed Ashby on the subject. Here is a good link
http://www.grizzlystik.com/Ashby-On-Momentum-Kinetic-Energy-Arrow-Penetration-W19.aspx

Killing deer is not so hard as our equipment has lots of power, but as you can see in my avatar I also hunt larger game with my crossbow and that has driven my position on arrow momentum.


Good Luck!

I’m actually a momentum person. With arrows over 400gs and speeds over 300’/sec, the momentum is there. Kind of like talking about horsepower verses torque. Turbo diesels such as the 3.0L Ram V-6 don’t have all that much hp but tons of torque from low to nearly max rpm. Even some of the turbo gas engines have what appears to be excessive torque (Ford 2.7 & 3.5 turbos). HP looks nice, torque does the work. KE looks nice, momentum does the work.
For deer and bear, I think if it’s 400gs and 300’/sec or more on each, the momentum is there.
If shooting the Micro 308, older Excaliburs, etc, it might be wise to consider heavier arrows to have enough momentum.