The Glock 21SF Generation 3 has some minor exterior design changes as compared to the Glock 21. The short grip frame is noticeably thinner from the backstrap to the trigger, and it incorporates the Glock Rail. It has an ambidextrous magazine release. Note the redesigned magazines will function in both designs, but the old magazines don't have the necessary cut out in the front of the magazines to function in the redesigned weapon.