There are lots of differences between inch and metric. With the exception of the mags most are minor in the grand scheme of things. Some parts are interchangable some aren't. Inch mags won't fit in a metric rifle as they have larger locking tabs. Metric mags will usally fit in an inch rifle but may or may not work. The cocking handles are different, same with the psitol grips. Rear sights are different. Inch ones will fold down and are in yards. Metric ones don't fold and are in meters, though ones on the canadian C1 are a compeletly different set up. Inch bolt carriers have sand cuts, metric ones generally don't unless they are the para models. The hammer springs are different. The safety bolt relese and mag relese are different. Same The gas block I belive is different though I am not sure. The gas regulator and cut off valves are different. The part that opens the upper and lower recivers I think are slightly different as well. I belive there are a few other differences as wll but I have to leave for work.