[Al Skierkiewicz]

If the terminal was flat but the wires still pulled out, the terminal likely was too large for the wire. The terminals are color coded for ease of use. Red for #18-#22 wire, Blue for #16-#14 and yellow for #12-#10.
If you were using the crimper that comes in the KOP, that crimper is designed for uninsulated terminals. It can be used for insulated terminals if one is careful. In either case (insulated or non-insulated), please note there is a concave part of the tool and mating bump on the other side of the jaw. When you set the terminal in the crimper, note that the terminal is merely a flat piece of metal that has been formed into a cylinder. The slit or open side of the terminal must be placed in the concave portion of the tool. If you set the terminal into the tool with the slit facing the bump, the bump will push open the slit and release the wire. If you are using insulated terminals, I suggest you purchase a crimp tool designed for those terminals.