Those FMJ bullets have the center of gravity rearward. Coming to a quick halt (eg. hitting tissue and stopping in 15-20 inches from 3K FPS) will exacerbate any yaw on that bullet and the heavy end will come around to take the lead in the bullet's terminal path. An analogy would be like putting the center of balance in a Corvette over the rear axle, and then slamming on the brakes at 180MPH and trying to turn at the same time...you'll be spinning in a flash.
It works with other cartridges too, but the 5.56 has the velocity to make it a more reliable outcome. Bullets that expand/fragment have that center of gravity move forward as the bullet's OAL shortens...usually keeping it oriented in the same direction it started.
I saw where it was stated above that the .22 tumbles...I would argue that a better term is "deflects" as it lacks the velocity/energy to penetrate bones most of the time.
This is a 15 page subject, so please excuse my brevity... If I left something out immediately vital, we can discuss as needed.
Im way late to this topic, but since you quasi-revived your own thread I figured that bumping my gums on this subject for a second wasn't too awful.
Glad you like the Punch offering. I bet it would work great for rodent dispatch.
