Most Boston Butts are in the range of 8 pounds with the bone in. The process in barbecuing a butt is pretty simple. Rub it, cook it, pull it.
First, start you barbecue and get it up to temperature, 220 to 275F.
Open the package and give the butts a rub with cheap yellow mustard. This adds some flavor and helps the 'butt rub' to stay on the outside of the meat. As for rubs, most any barbecue rub will do. However, I like to use a rub with little or no sugar in it as the butt turns out a deep red color instead of black, as it will if you use a rub with a lot of sugar in it.
Whatever butt rub you use, give the outside of the meat a generous rub with the spice blend.
OK, so you've got your butt rubbed, put the meat on the cooking grill and covered the barbecue. Every 2 hours, turn the butts over and rotate so no side gets too much heat. I no longer mop or baste my pork butts as the fat on and within the meat self bastes them. If you want to mop, by all means go ahead. You can use a mixture of 50:50 canola oil, apple juice and a tablespoons of your butt rub. Mop the butts when you turn them.
After 8 hours of cooking, I will usually stick the temperature probe into the meat. It's done when the internal temperature is above 190F. This temperature will arrive faster the higher the temperature you keep the cooking chamber. Slow cooking is the best method to arrive at a moist and tender Boston Butt.