RE: Sighting in a riflescope
Loony, you're correct... If you can fire one shot, make an adjustment, and then fire consistently at 300 or so meters, then that's all you need to do. In the hunting world, shots are rarely attempted at a greater distance than 300 to 400 meters, so this is practical.
Stubble, you're correct... I was taught to make an adjustment only after firing atleast a 3 round shot group, and I practice this consistently. It would never do for me to fire one shot, and then make one adjustment. BUT, that is because I usually fire at a greater distance than 400 meters.
You're both right, so there.