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Author Topic: Angle of Incidence  (Read 103 times))

Offline BinjiC0d3r

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Angle of Incidence
« on: August 01, 2022, 02:20:01 AM »
So here is something that I feel needs to be discussed as we start to take game at longer distances. The phrase, Angle of Incidence first came to my knowledge in the early 90's as I was working on an optical full duplex PCMCIA communication card for a beautiful technical show car we would use for all of the up and coming automotive technologies at the time. Let's call this vehicle, the Purple People Eater. The PCMCIA was a modern dedicated parallel communications port used in laptop computers, so we developed our communication interface with an infrared transmitter at 880nm and  a receiver at 930nm.  I crafted a similar communication device cleverly hidden in the vehicle's tail light, but it had a transmitter at 930nm and a receiver at 880nm. I used an infrared transparent piece of plastic in both devices, and we opted to use just once piece instead of splitting the plastic in two, for aesthetic reasons.

This worked well in the initial design, but at a further iteration, the TX/RX diodes were moved back from the window, and the Angle of Incidence just happened to be at the critical angle, and none of the infrared signal would be emitted from the led to the outside world.

So Ed, what the heck does that have to do with Airguns!!! Well, I'm glad you asked!  ;)

At long distances that have a more loopy trajectory, the projectile also has an angle of incidence to the prey. When that angle is at 90 degrees, all of the energy that the projectile has is expelled into/onto the game. But as that angle is reduced with more loopy trajectories, the effective energy is reduced.

In the first half of the video below, I shot a groundhog at 95 yards, and I was aiming for it's head. The travel time for the .30cal FX Hybrid Slugs traveling at 930fps is only a 1/3rd of a second, but that was just enough in addition to the MOA accuracy I have with this round to put the round 6 inches behind the intended target. So instead of a 90 degree angle of incidence, I have a maybe 20 degree angle. At the reaction of the game, I though I landed a fatal bodyshot to the spine, but actually, the result was a non-fatal glancing blow. I discovered this because for some unknown reason, this guy decided to close the distance and get taken out at 30 yards, and that's when I discovered the previous wound shown in the photo below.

As we strive for ethical pest removal, we must take into account the Angle of Incidence of the round to the prey to ensure we deliver deadly, not wounding shots.

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Offline customcutter

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Re: Angle of Incidence
« Reply #1 on: August 01, 2022, 09:40:14 AM »
Excellent point Ed.  I've never done any long range pesting.  Just as we plan for a quartering shot to angle through the vitals, we should learn the trajectory of long range shots and aim just a little higher to account for that downward angle when the projectile reaches the target.
  • Valrico, Fl