Rifles and ammunition
At the start of the project the choice of calibre generated a great deal of discussion with both the pilot and thermal operator supporting using the larger .308 calibre AR10 instead of the AR15’s smaller .223 round for this task. Their reasoning being that the .308 had far more energy and the heavier projectile would potentially have less deflection and penetrate the canopy without “blowing up” if it hit vegetation on the way to the target. This was a largely true observation.
 
However, the AR15 has a lot of advantages over the AR10 platform. The AR15 rifle is approximately 30%, lighter than the AR10, therefore far easier to compensate for sudden changes in direction of the target animal, and it has significantly less recoil, muzzle jump and muzzle blast which means the shooter can shoot it faster and more accurately. This is contrary to the preconception by many hunters that the faster .223 bullet would deflect easily or fragment after hitting any leaf or twig and would not be as effective with body shots on deer sized animals.
 
The rifle that was used during this trial was a customised AR15 platform with a red dot optic (Aimpoint T2 Micro). This setup worked very well for fast shots but was only effective once the deer was in the open and could be visually identified by the shooter. The 62gn Federal Fusion .223 ammunition we used was very effective at penetrating the canopy and killed deer every bit as effectively as a .308. This was due to the 1:8 twist imparting a lot of spin and stability to a long, well-designed and well-constructed projectile. Ultimately, the firearm type and construction evolved and a custom-built ‘thermal firearm’ was developed.  It’s full evolution and development is outlined in the Appendix.
 
Helicopter crew configuration