@g2outdoors
WARNING: long ranting post, tl;dr - consider using a lighter shaft and front load it with heavier components
I'm working through my second iteration of a heavy arrow build. My old setup is as follows:
- 27 inch black eagle deep impact shafts (.165 ID - 11 gpi) - 297
- black eagle ss outsert - 68 gr
- 100 gr broadheads (single bevel)
- vanes + nock + wrap - 58 gr
Which leads to a finished arrow weight in the 525 gr range (give or take how much glue I used for the vanes). I wanted a heavy arrow to follow the same logic of being able to use any generic broadhead I wanted. My bow is well tuned and is bareshafting bullet holes through paper. I never paid too much attention to FOC because I figured as long as my arrow is flying straight and true the inertia would do the rest of the work for me.
What I learned was that I was
WRONG! My last buck I shot this year I shot at 30 yards with a slight quartering to angle (5 degrees if that). The entrance was perfect with a nice hole in the "vital v" between the humerus and the shoulder blade, however on exit the arrow barely clipped the offside lung, took out the liver and popped part of the diaphragm. How could such a heavy arrow deflect
that much? The Ranch Fairy talks about this: animals MOVE! On impact the buck was starting to duck and turn, not much, but enough mass/movement to redirect the path of a heavy arrow out of a 70 lb bow.
I fully understand that this is anecdotal evidence, however it got me thinking more about FOC. Some people (Ranch Fairy included) claim that higher FOC will "pull" the arrow through. As someone with an extensive background in mathematics and has a healthy understanding of physics, I really can't get behind that statement. There was a video (which since has sadly been taken down) on youtube titled something like "FOC penetration myth debunked" made by an engineering student. He assembled multiple arrows with identical weights and varying FOC and then shot them into ballistics gel. His findings showed that changes in FOC did NOT yield different penetration. The evidence provided a stark contrast to the idea that foc "pulls" the arrow through the medium.
If that is the case, why is it perceived that higher FOC yields better penetration? Thinking back to my own experiences, and running some thought experiments, the answer starts to come into focus. Again, animals
MOVE. Target mass moving orthogonal to the path of the arrow imparts deflective forces on the arrow at the point of impact. So FOC doesn't necessarily "pull" the arrow as much as it gives the arrow a better
MECHANICAL ADVANTAGE to
RESIST deflection/deflective forces. As a simple experiment try opening a door by pushing by the handle, pretty easy to move right? Now try opening the same door by pushing as close to the hinges as possible, a little more difficult isn't it? Higher FOC places the center of gravity (and hence the fulcrum) closer to the point of impact.
I invest time and money building heavy arrows in the off chance that if something goes wrong with the shot I have enough inertia to penetrate through something hard. Since I'm already investing resources to mitigate risk for one scenario out of my control (needing to penetrate through bone), why not also mitigate risk for another scenario out of my control (deflective forces) at the same time?
That's why this year I'm going with a lighter arrow (black eagle x-impact 8ish to 9ish gpi) and heavier components (ethics insert/outsert system - 120 to 180 gr) to not only maximize inertia but also maximize FOC. I've already ordered the ranch fairy kit from ethics and a couple of shafts from lancaster and will be working on my off season "handloads" over the next couple of weeks. This year I'll be targeting 550ish grains with a 100 gr broadhead for whitetails but will be experimenting with the ranch fairy kit so that I'll have enough spine headroom to slap a 200gr broadhead on the end for elk this September.
HOLY CRAP that was a long post! If you actually made it to the end I thank you. Good luck with your heavy arrow journey, I look forward to the content that will inevitably make it to youtube!