So here is the deal. I inherited two AR-15's. One is a stock Colt AR-15 (Mil spec with standard everything) and also a Bushmaster AR-15 with short barrel and telescopic stock. I had the "bright" idea of switching the barrel's and stocks because I wanted the Colt with the shorter barrel. But much to my dismay I can't remove the stock from the Colt AR-15. It is an older model, so is this just the way it is. Also, I can't remove the upper receiver from the lower receiver. What the heck is going on? The Bushmaster comes apart no problem.