Looking at their website, the Mil-Spec is exactly that: a standard 1911A1 modern military specification with a regular grip safety, military sights, standard hammer and trigger, etc. The Full-Size is a "modernized" version of the same basic gun. The picture they show is a "Custom Loaded Full-Size" so it's a little unclear as to how many of the features it has are included in the base Full-Size. I think we're talking modern low-profile fixed combat sights (nice sight picture), a beavertail grip safety (if you've had hammer bite you'll appreciate that), lightened hammer, modern trigger (same pull as the Mil-Spec though), and front cocking serrations as standard. Then you can choose add some features to it like adjustable sights and various finishes.