I once had my Krieghoff .458 WM double on me. I did not have two fingers in the trigger guard and it didn't strum fire, since both holes in the target were only about an inch from each other. When a rifle doubles, the recoil doesn't double, it quadruples. The recoil is related to the square of the recoil velocity, and when the velocity doubles, as with a double, then the recoil energy is four time as great. Nevertheless, I didn't fall down or lose control of the rifle. I took a step backward and my feet got tangled up and I went to the ground. Both the rifle and I were undamaged.

We could only conclude that a bit of dirt had somehow gotten into the action, because after a good clean, it has never doubled again, and that was fifty years ago.