Internal is on the inside of the slide, just as Mr. Browning designed it for the 1911. The external can be seen on the outside just behind the ejection port, take a look at any Glock or new Kimber. The external is considered better as a rule, more reliable plus easier to service. But on the other hand...Kimbers did work fine until they switched to the external now they are having major problems. Some gun companies just know how to make the external work, such as Glock and S&W. Some know how to make the internal work, such as SA and Colt. :wink: