Retch in your broadhead studies or observations have you ever witnessed or tested what a good sharp cut on contact 2 blade head would do out of set-up with high amounts of KE? You see on tv all the time these guys lob these arrows out and hit deer in the spine with only what appears to be 4 inches of Penetration and the deer drops. Would a more traditional orientated 2 blade head have gone through the spine and bone or just bent and deflected with the added KE?
Bone is a mighty force to be reckoned with. I have little experience with the new high speed/high K.E. bows in a hunting situation. My fastest bow and the one that develops the most K.E. is a 2006 BowTech Justice that delivers my 363 Gr. arrow a blazing 263 FPS for 56.8 Ft/Lbs. of K.E. I took 4 deer with it in 2006 before I put it away to use a homemade longbow. I haven't looked back since but in all my travels with my chronograph, I can see that today's new bows like the Mathews Reezen, Monster and Z7 as well as the comparable Hoyts and BowTechs and other bows are producing 70 and more Ft/Lbs. of K.E. making those shots that hit bone more likely to result in a harvested and rcovered animal and thats a good thing. Because I process a lot of deer for hunters, I come across a lot of old archery wounds (including shots in the spine, legs bones and even the skull).
http://www.archerytalk.com/vb/showthread.php?t=718489
Because I expect at come point to hit bone, when I started making my own broadheads, I set out to test them on direct bone hits. You can see that at this link.
http://www.archerytalk.com/vb/showthread.php?t=717523
I have friends with more money than I do so they make more out of state hunts but because of my life long facination with aroowheads and arrow lethality, they will on occasion, come to me for assistance. This is one such example of a fellow going after 1500 pound American bison with a bow. (this is the same guy with the broadhead in the brain buck posted above) Here is how we tackled his challenge with the proper arrow and broadhead.
http://www.archerytalk.com/vb/showthread.php?t=717435
Sorry to ramble but back to your original point. A spine hit with an arrow, almost always results in the arrow failing to pass through. I think that is for a couple of reasons. Most people shoot 3 or 4 bladed heads making it almost impossible for all the blades to pass through the bone and out the other side of the deer. 2nd, the deer moves on impact (actually starts moving in most cases, prior to the arrival of the arrow) this means a great deal of energy is lost in a upwards, downwards, sideways or twisting motion of the deer. That loss of energy prevents a pass through on bone. 3rd, deer are flexible and by that I mean, elastic. When a arrow hits something like the spine, it pushes and bends the spine in the direction of the arrow. Sort of like hanging a bag target and shooting it with an arrow makes the bag swing upon impact. A shot on a deer that misses all bones creates a pass through that takes place so quickly that sometimes even the deer is unaware that it has been hit. Add a bone hit to the equation and you get a less desirable outcome that pushes the bones in the deer sideways. This will sometimes knock the deer off its feet from the impact force.
If today's bowhunters using high speed and high K.E. bows would capitalize on the efficiency of these new bows, they would hedge their bets in regards to a potential bone hit by using a heavier arrow (500 grains or more) and they would use a 2 blade head such as the Magnus line or the Muzzy Phantoms (without the bleeder) or any of the Zwickey or sliver flame heads. These modern bows with a 500 grain arrow and well built 2 blade head could turn that super speed into super K.E. and momentum and penetration and not fear any bone (in the vital chest area) on deer sized game. Sorry to go on so long but this is a subject I have been interested in for decades.
In a little over a week, the WBH will hold its annual broadhead shoot in New Lisbon, We offer attendees the ability to shoot through our speed/K.E./efficiency station. I look forward to the results from this years testing. There will be hundreds of bows sampled and I expect the average efficiency number to go up. For the last few years worth of testing, the average efficiency has been .843. I would expect that to be edging towards .9 or higher. It's interesting to talk to bowhunters and to hear why they choose the broadheads they use. Much of it is market driven rather than based on actual data. We don't allow mech heads to be used on the course or in the Ultimate Broadhead Challenge because of the 7/8 inch min width and 1 1/2 max width rule and the fact that those that use mech heads cant or wont lock their mech heads in the full open position but mech heads and pass throughs and lethality are another topic all together.