I'm not at all detracting from the importance of shot placement charts, but if I could make a suggestion: The issue I have with charts is that they aren't particularly helpful for angles that aren't perpendicular (which is ideal). So, I learnt to visualize a ball the size of a rugby ball in the middle of the front half of the ribcage and to aim to hit that. It's served me quite well, having only had one botched kill (which was due to jerking the trigger). That rugby ball allows me to compensate for almost any angle and has helped me pull of some pretty undesirable shots when following up on wounded game. Any shot on a wounded animal is justified, for me. The sooner the animal is out of pain, the better, but it's important to be able to take full advantage of any opportunity he/she gives you.