I understand the the concept of speed/lightweight vs slow/heavy. We all can grasp speed/heavy combo. I would like to know if there is a way to calculate the magic window of effeiciency when you go lighter/faster or heavier/slower you start to lose penetration. If I take my 60#@28" bow and shoot a CE Heritage 150 with total arrow weight about 440gr., CE Heritage 250 wtaw about 640gr. and a CE Heritage 350 wtaw about 733gr. there has to be one that will out penetrate. I know it won't be the 150, everything tells me it would be the 350 except the results into the same target in the same spot. There has to be a window where the combination of speed and weight are optimal and more of one or the other gives deminished returns. YES or NO? If so, how can one find that magic window of the greatest return for speed and weight? Is distance the key factor? If so, is there a way to calulate the max distance before deminished returns for these combos?

A long time ago I asked the same question and was told to find it thru kinetic energy. This energy is determine by both mass and speed;
KE=Mass X Velocity x Velocity / 450240
Kinetic energy equals mass times velocity squared divided by 450240(use calculator to remain sane). I used a chrony at star6t for six shots of each sample then at 18 yards to determine loss of speed and calulated at both spots to see which arrow combo had kept the most energy at that distance. I am sure someone can answer this easier but this has worked for me. Results will amaze you as this will give you potential energy to penetrate.

IMO I think that the heavy arrow off the string will be slower than the others.Some guys use different setups for different animals.(A 733gr.arrow on a squirrel=overkill).I feel it is all about what you are using it for.Compare all three at 20yrds in the same target with the same points.And then paper tune them to see the different flight from right out of the bow to see what that difference is.There are so many variables,bad release,wind and many more.Im sure you will get a ton of opinions on this But I prefer the keep it simple for what your hunting purpose is.

For me,
The old rule of 9-10grs per pound works best.Gives me excellent penatration,even w/ big snuffer, along w/ decent trajectory.I shoot bows in the 60 to 70 lbs range and have killed deer w/ 405to795gr arros.They did their job but like the feel of my bow at the shot w/ the formula above.

You also have to consider that once the arrow and broadhead make contact with the game, that the lighter arrow will shed kinetic energy at a much faster rate than the heavier one.  Putting it to extremes, think of it like this. If at ten yards I throw a ping pong ball at you as fast as I can or lob a golf ball at your noggin, which is gonna do the most damage? If you can shoot more arrow weight without giving up too much in speed and trajectory over the light setup, then it is to your advantage to go heavy for penetration.

I don't know how to do the math, to answer your question, but I have a feeling that by the time you found the dimishing return the trajectory of the arrow would be so great as to be impractical for hunting.  Just a guess.
I've done some of this type of testing and have noticed that the trajectory itself begins to become a factor as the arrow angle of attack becomes great enough that I have to tilt the target block to get fair comparisons to the lighter arrows.
My target block has thin layers of foam that grab the arrow as it slides between them but if the angle of attack is great then the arrow begins to cut through the layers.

Still, the very heavy arrows still out-penetrate the faster ones.

overkill ?? what is overkill ????  

To be effective, you need velocity and mass.  For some reason, speed has always been the star when it comes to marketing.  The key is to find good velocity casting a heavy arrow.  A heavy arrow will maintain it's energy at distance whereas a light arrow will shed energy faster.  Bascially, we are talking momentum.  It that tortise and hare analogy.

A long time ago, I shot an arrow I made up that I was using in my 70@28" Strunk Spirit LB.  The arrow weighed around 615 grains and was a Doug Fir shaft, had a 160 Grizzly BH and 3-Maxi fletch.  I draw this bow around 27.5 so I figured I'm around 68#.

I shot this set-up into a lid on a 55 gallon steel drum @ 40 yds.  The lid is 18 gauge (0.050" thick) low carbon steel. The 160 grizzly BH penetrated slightly over 1 inch into the lid and the arrow did not break.  Still useable!  The only damage to the arrow was the tip of the Grizzly had a slight bend, which was easily straighten on an anvil.  BTW, this was a Grizzly head that was purchased when Elburg was making them.  No modification to the BH.

My point is a 600+ gr arrow traveling maybe 170 fps has a boat load of energy.  I could see this arrow plowing thru a shoulder of an elk with no problem.  Bottomline, use top of the line components,  balance out speed and mass and you will have all the energy you need.  There is something to be said of the 9-10 grain per pound rule.

Mike

Out of one bow,assuming good arrow flight and all other things being equal,the heavier the arrow,the deeper the penetration.The only diminishing returns are that at some point,heavy will give you a trajectory that you don't like.You just have to decide on the combination that gives you the trajectory you want.

For most people,that 9-10 gr is good for that.

I have been shooting arrows that way 13 grs and at 20 yds,trajectory is no big deal.At 25 I have to raise it 4" more.

If you want to shoot 30 yds and farther,you will have to adjust but at the ranges that most of us impose on ourselves,that weight isn't a problem and I see big gains in penetration.

It's just a matter of finding the happy medium for you and what someone else uses really doesn't matter.

If I can get an arrow tuned perfectly and it falls between 10-12gpp I'm good to go. Most of my bows are #55-62 at 30", an arrow that is between 600-750 just work well for me. Good tradjectory at hunting ranges, quiet, gets rid of any handshock. I've heard that most bows efficiency peaks between 11-121gpp.

Eric

All this input is very helpful! I appreciate you all giving me your time and sharing your thoughts and experience. I have been able to put this together with some resolve in my mind. Now I can use it to see how it will work for me. Anyone else willing to share, please do, I'm still listening. Thank you.