I have a 10 round Baretta 92 magazine. It appears the only difference between it and the regular 15 round magazine is the spring. It seems fully compressed with 10 rounds, not allowing any more rounds. Also on the back of the magazine are holes for 4, 7 and 10 rounds. These are the exact same spacing as the holes for 5, 10 and 15 on the 15 round magazine. Can anyone explain this? Can I simply replace the spring with one for a 15 round magazine.