RE: knockdown power... fact or myth?
I cant see newtons law applying to this, the rifle's weight messes that up. A 30-06 bullet shot from a 5lb and 15 lb gun will be very different in recoil, but will shoot the same out of the barrel. so the action is the same, but the reaction is different. the 5lb rifle may not knock you down, but the 15lb rifle definetly will not.
The initial force of the reaction is nullified by the weight of rifle, as the bullet flies clean with nothing to hold it back. So the force of the bullet is harder than the reaction of the recoil.