That's very interesting Rebecca... I've never experimented with lower draw weight/shorter draw setups and very heavy shafts, but I've never seen KE or Momentum numbers decrease as a result of adding weight to the arrow. In my experience - both increase with mass - always... and frictional forces that stop the arrow in a target decrease with reduced arrow velocity. Your setup seems to defy the laws of physics regardless of which theory you subscribe to.
Were you forced to use different arrow diameters in your testing to achieve different arrow weights? Arrow diameter is a HUGE factor in penetration so could that have skewed your results?
Interested...
Coop
Yep Coop it makes sense that heavier arrows would have better penetration, but in preparation for my dangerous game hunt, we bought the Alaskan Grizzly sticks along with 315 grain tips and shot them out of my bow and my husbands bow that has more draw weight. We shot for months recording all our results by video and on paper. The bottom line is….when you increase the weight of an arrow... there is going to be a point at which the velocity begins to decrease, which in turn decreases KE. You can see this when you run the KE values.
With a 60lb bow shooting a 300 grain arrow, IBO is 330, draw length 28 in. on the KE calculator the resulting KE is 60ft. lbs and speed is 299 ft/sec.
In turn, same bow, same set up but 400 grain arrow the resulting KE is 64 ft. lbs KE and 269 ft/sec
425 grains is 65 ft. lbs. KE and 262 ft/sec
430 grains is 65 ft. lbs. and 260 ft/sec
435 grains is 65 ft. lbs. and 259 ft/sec
440 grains is 65 ft. lbs. and 257 ft/sec
445 grains is 65 ft. lbs. and 256 ft/sec
500 = 63 ft. lbs. KE and 239 ft/sec
600 grains = 58 ft. lbs. KE and 209 ft/sec
700 grains = 50 ft lbs. KE and 179 ft/sec
So referring to the bell curve….there is a sweet spot where it plateaus and reaches the optimum KE and speed before it starts to drop off. In this set up it would be between 414 grains and 448 grains. The KE is at the plateau of 65 ft. lbs. with 414 grain arrow shooting 265 ft/sec and 448 grain arrow shooting 255 ft/sec.
We found with our penetration tests that penetration mirrored this mathematical bell curve.
You can use these same calculations to set up a bell curve with your bow.
I would be happy to send you the Alaskan grizzly sticks with the 315 grain broadhead for you to test and see what you think (send me a PM with your address). We were told that this was the way to go for the best penetration. But that is not what we found. The results were not what we expected either, but we watched it happen shooting in to various targets. I am still testing MANY different arrows, broadheads, weights, etc..because I am determined to find the set up that will provide me with the most KE and velocity that will give me the most penetration. This is crucial for me because I cannot pull 80 or 90 lbs. I have to test all of this. I do not want to go hunt dangerous game and not be completely prepared.
So it may seem that my set up defies the law of physics….but try it out yourself.
As far as the arrow diameter. I am using VAP arrows because of the small diameter. The small diameter decreases drag upon penetration, and they ALWAYS penetrated better for me. The grizzly sticks have the same idea because it is tapered front to back, but it is a much larger diameter which will increase the drag.
I am currently working on a very in depth article to show what I found. Everyone is still going to have their own theory and that is how it should be. But this is what I found not only by physically testing it, but backing it up with the KE calculations.
This subject causes a lot of debate among archers, and the way I feel about it is…..you need to find the set up that performs the best for you based on what you are looking for. My normal bow set up is very different than my dangerous game set up. It may be speed, it may be KE, it may be penetration.
Its a fun subject! I would love to hear what other people have found in their testing. But as Nick said, archery is a very simple concept and most people really don't need to worry about these details.
