Several months ago, for my birthday, a relative gave me a vintage Colt factory magazine for my 1938 First Series Woodsman. When I finally used it yesterday I was a bit shocked to see the slide lock back after the last round ejected. Not supposed to happen on a 1st series. First I thought I had a jam but upon closer inspection saw that the follower was raised up far enough to capture the bottom of the slide and keep it open. I loaded and shot it several more times with the slide locking back on the empty magazine. When I disassembled the mag and checked the follower against another it measured a few millimeters taller. Enough to catch the bottom of the slide and keep it locked open after the last round fired. Of course to drop the mag I needed to slightly pull the slide back. This was not a reworked Colt follower but definitely an aftermarket taller replacement. Someone had to have been selling these at some point in the past. First time I've seen one. It was rather cool not to have to count rounds and just have the slide lock back. Has anyone ever come across one of these? Also wondering whether it's a bad idea using this as might it eventually cause wear on the bottom edge of my slide where it hits the follower.