deer hunter 21

i was just on bowjacksons website trying to figure out the energy on my arrow and everyone always told me that the hca speed pro arrows would not have enough energy well when i figured my 350 gr arrow at 280fps i came up with 61lbs and when i i figured my speed pro 300gr arrow at 315fps i got 66lbs so now i'm confused everyone was telling me that the speed pros would not have enough energy to hunt with but it looks like its putting out more energy than my carbon express 300cx so now i'm really confused cause i like the speed of the speed pros cause i have a short draw length can someone please help explain this to me. thanks alot

adams

KE=(weight(350g)/450240)*(velocity(280fps)*(velocity(280 fps)
350/450240=.00077736318 * (280*280)=78400
.00077736318*78400 =60.945273312 Call it 60.95 ftlbs

(300g/450240)* (315fps*315fps)
(.0006663113)* (99225) = 66.1147387425
Call it 66.11 ftlbs

Your calculations are correct. You generate more energy with with speed pro arrows. It is not uncommon for a heavier arrow to generate more down range energy. This appears to be a case contrary to popular belief. Did you actually chrono the diffrent arrows?

Arthur P

Assuming both arrows are the correct spine for your bow, there is no possible way that dropping 50 grains is going to account for 35 fps difference. You need to run those arrows thru the chrony again.

silentassassin

Did you verify the speed gain by chrono? The vast majority of solocam bows would only gain about 16-17 fps by dropping 50 grains of weight, some how you manageed to gain 35 fps by dropping 50 grains of weight which every knowledgeable tech in here would tell you is a physical impossibility or at the very least EXTREMELY uncommon. By dropping 50 grains you should either stay at the same KE level or lose 1 foot pound or so. I think you need to run things through the chrono again and verify wieghts on a scale. The laws of physics don't bend for speed pro arrows or any other kind. JMO

Bees

That doesn't look right to me either. those speeds don't appear to jive. With my bow a 100 grain change in arrow weight yields somewhere around a 30 ft per second difference. A 50 grain weight change yields about a 15 foot per second difference. Something ain't right with his numbers.. either his heavier arrow is going faster or his lighter arrow is going slower than he thinks.

Physics is physics out of any one bow weight and draw length combination, a 50 grain heavier arrow going a bit slower will always yield a bit more KE than the lighter arrow going a bit faster.

Ain't going to change just so you can say the lighter arrow has more engery

deer hunter 21

you guys are right about me being wrong but the speed was correct but i had my arrow weight was in wrong my weight should be 275gr speed pro and i did the test again and actually lost a 1lb of energy now i understand i just messed up and calculated my arrow weight wrong sorry to bother you guys thanks for the help though.

silentassassin

No bother deer hunter 21. Some of us have just done that so many times that we knew there was something wrong. Glad you got everything figured out.

adams

No worries. It's all about learning as much as possible.

Paul L Mohr

You are looking at speed and ke figures and forgetting about momentum. The figures you are looking at are like looking at muzzle velocities out of a gun. This is what the bow will do a few feet in front of it. Those are some REALLY light arrows. The heavier the arrow is, the more momentum it will have. Thus retaining more of it's energy farther down range and actually hitting the target harder. Lighter projectiles bleed off energy faster losing KE at farther distances. The differences may not be enough to worry about at 20 or 30 yards however, I didn't do the math. I would personally go with a heavier arrow and shoot around 250 something to retain more energy down range. That however is a personal preference, I'm sure others would dissagree with me.

Just something to consider any way.

What kind of bow and what settings are we talking about here? What is your draw length and weight? Just curious.

Paul