Hello, I just bought a model 39-2 and was wondering if someone could tell m e about the different followers used on this magazine. I still have a magazine from a previously purchased 39-2 and it has an "X" shaped metal follower. The follower on the 39-2 I just picked up has a plastic follower. The mags otherwise look identical. Did S&W switch to the plastic follower after a certain date? Thanks.