You just have to remember a hogs anatomy is a bit different than a deer Clem. The lungs are a bit smaller and they are angled more upwards and also a bit further forward. The heart also sits a bit lower in the body than that of a deer. Also, if a frontal head shot is presented, and that is the only shot, aim about 3 inches back from the nose. While a hogs scull is not armor plated, it is fairly tough with fairly thick and tough hide and severely angled. Most believe that they have very hard and thick sculls but in truth, they are fairly thin. It's the angle of the bone structure that defeats some shots. Hit them at "the bridge of the nose" ,for lack of a better term, and 90% of the time it will drop them right there on a frontal shot. If quartering to, go for about an inch under the shoulder point for a heart shot like falcon was presented and executed perfectly. This right here is a good example of good kill points for broadside:



And this is a fairly accurate anatomical drawing for heart and lungs: