IMO there isn't a better setup out there than a Trypan for killing elk out of the right bow, with the OP's set up it will work awesome for him. Shooting a 500gr+ arrow out of a 70lb bow with a COC head you are taking all of that energy and putting in the dirt behind the animal. Now if your shooting lightweight arrows or a super short draw sure put a COC head-on. The last elk I killed with a COC head I shot with a 400gr arrow and that arrow zipped through the elk so fast and far that we never found the arrow, it also left a crappy blood trail just like every other elk i've ever killed with a small COC head. The only elk I haven't gotten a pass-through on was one I hit directly in the shoulder socket at 20 yards with a 67lb CST, Easton Injexion with a Slick Trick head, I got trail cam pictures of that bull two years later, I honestly don't think an arrow on the planet would have saved me on that shot.
River Rat, There is a great thread on Archery Talk in the Western Hunting section on the Trypan used specifically on elk, I can tell you from personal experience that they are devastating and very durable. Shoot what you are comfortable with and gives you the most confidence, the Trypan is more durable and well built than a lot of fixed heads I've shot and hold up just as well or better.
This arrow was shot as a follow-up shot, it was a hard quartered toward a shot at a dying bedded bull from 30ish yards, the arrow went through a pile of muscle, the front top of the shoulder plate, the very top of his ribs, his windpipe and stopped inside of the elk at the back of his vitals. The arrow was 480gr shot from a 74lb CST with a 27.5" draw. You can see the crease of his front shoulder right above my fingers in the picture, the first picture you can see where the arrow went into the upper ribs behind the front shoulder. I didn't get a picture of the shoulder when I was butchering the elk, this year I will take more pictures on the two bulls we kill with Trypan.
The first arrow was a pass-through but lower than I would have liked right where the diaphram meets the vitals, as soon as I hit you could see blood running out like a garden hose, the bull walked 20 yards and laid down while all 30 of his cows ran off. He would have easily died from the first arrow but I am of the belief that if they are still breathing and you can you should put another arrow in them.
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The head still spins true and the only thing wrong is that the tips of the blades are slightly bent back, I am keeping it as a practice head and honestly, they are super easy to sharpen and I would have no issue shooting it again.
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