HELP ME CHOOSE AN ARROW WEIGHT/BROADHEAD SETUP

[Mighty Mouse]

At some point on the chart your KE will peak before beginning it's downturn.
That will be YOUR arrow setup.

That’s incorrect. KE rises continually with increasing arrow weight. KE does not peak at a certain arrow weight then drop thereafter. Any calculator that shows a peak in KE is flawed. The calculator on the Ashby Bowhunting Foundation* website correctly accounts for the relationship between arrow weight and KE, but many calculators out there do not.

Also, KE is completely irrelevant to arrow choice. For all practical purposes, your draw weight, draw length, and bow choice determine your KE. KE does increase slightly as you increase arrow weight, but the increase is negligible and should not factor into arrow decisions.

*Fair warning: ABF is a group of heavy arrow, high-FOC nuts, and they put out some very bad advice. Their online speed/KE calculator is, however, sound in its underlying math/physics.

 

[lil' bear]

That’s incorrect. KE rises continually with increasing arrow weight. KE does not peak at a certain arrow weight then drop thereafter. Any calculator that shows a peak in KE is flawed. The calculator on the Ashby Bowhunting Foundation* website correctly accounts for the relationship between arrow weight and KE, but many calculators out there do not.

Also, KE is completely irrelevant to arrow choice. For all practical purposes, your draw weight, draw length, and bow choice determine your KE. KE does increase slightly as you increase arrow weight, but the increase is negligible and should not factor into arrow decisions.

*Fair warning: ABF is a group of heavy arrow, high-FOC nuts, and they put out some very bad advice. Their online speed/KE calculator is, however, sound in its underlying math/physics.

KE=1/2M(V)^2
Velocity matters more than mass. You cannot continually increase mass to increase KE.

You are somewhat correct in that KE does not produce wound channels with arrows. HOWEVER most mechanical broadheads take around 40ft-lbs to open. Some are as high as 60. If you only have 65 pounds and your broadhead eats 55lbs you are what we call Fuc%ed

 

[Questionablemorel]

I've personally had great experience with a 450 to 475 grain arrow. Balance it well with your draw length and poundage, you can shoot 3d events and hunt a variety of species.

 

[Mighty Mouse]

You cannot continually increase mass to increase KE.

You absolutely can, but the KE increase is small and inconsequential for all practical purposes. Below are two datasets based on arrow speeds I personally chronographed (not estimated from a calculator) that show KE continually increasing with arrow weight. You can find many other datasets showing the same KE trend if you go digging.


A bow is an energy conversion machine; it transfers the energy put in by the archer to the arrow. The bow's potential energy developed during the draw cycle is primarily a function of draw weight, draw length, and brace height. Cam profile and let-off percentage also have an effect. Once those parameters are set, the bow's PE is set. PE can be calculated by plotting a draw-force curve and calculating the area under the curve. Below is an example from my old Mathews Heli-m.


The arrow's KE is equal to the bow's PE minus energy lost to friction and to accelerating the string/cams/limbs. The bows I've tested have shown approximately 85-90% efficiency at converting PE to KE. As the arrow gets heavier, everything gets slower, and less energy gets lost to acceleration of string/cams/limbs. PE is still fixed, but losses are reduced; thus, energy transfer efficiency increases (slightly) and the arrow's KE increases (slightly). I've seen this behavior with every bow I've ever tested.

If you have a few hours to kill, here’s an old thread on Archery Talk discussing this topic ad nauseum: https://www.archerytalk.com/threads/peak-ke-and-arrow-weight.6172572/#replies

 

[Bill V]

I've passed through the knuckle on two mature bucks with this setup:
RIP TKO 250, 75 HIT, 10 grain Impact Collar, Iron Will Wide Single Bevel 125