A full pork shoulder consists of two halves, the 'Picnic Ham' and the 'Boston Butt' and can weigh 8 to 20 pounds. A picnic ham is not a true ham but a roast that runs from the shoulder socket through to the elbow. True hams come from the rear legs only. The picnic usually weighs from 4 to 12 pounds. The top half of the shoulder, that being the roast from the dorsal of the animal near the spine through the shoulder blade, has way too many names: Boston butt, pork butt, butt, shoulder butt, shoulder roast, country roast, and the shoulder blade roast. Why the heck we call it a butt seems ironic, I mean it comes from the front of the hog for crying out loud.
In case one wonders what all goes on inside the cover of that smoker (even when cooking off-heat on a grill) and what it takes to ensure a bodacious roast, here's what I know. Ideally you want to maintain the inside of the cooker at a temperature between 225-240 degrees F. On average, given the fact that roasts take between 1 to 2 hours per pound to cook, there is a stalling period or plateau at around 155 degrees during which the internal temperature of the meat levels out without much change in the temperature. During this stage the energy from the heat goes about doing its thing, breaking down the connective tissues, collagens and the fats while moisture moves toward the surface. This is what in layman's terms we call 'making it tender.' If you are able to gauge the internal temperature with, say a digital thermometer, you will not notice any changes for a long period, not until most of the internal tissue starts to really cook and the fats are rendered will you notice the temperature starting to rise again.