I'm getting more and more familiar with 1911s, but I've realized I have no idea how the different sizes work. I know only that the government size is the full-sized firearm sitting on my desk. I hear of commander and officer sized guns/parts, but don't know anything about them. Could anyone explain to me the difference in models? Are they interchangable (as in, can you put a government slide on a smaller frame, or vice versa)?