I bought a magazine at a gunshow that the seller & I thought was for a 3913. However, it is about 3/8" shorter and is only a 7-rounder, and from the looks of the follower, it's never been used. I'm guessing it's for a CS-9 or a Shorty-9?
Anyways, I have neither pistol nor use for it. I paid $37 for it and if anyone wants it, I will ship it to them for that.