Look on here- it’s about slightly bending the feed lips in for the slightly smaller 9mm- like .5 mm. Also gets bonus of loading 12 rounds from what I understand.
I wouldn’t do it for you- probably need to work it a little and make sure your gun handles it.
Maybe I haven't searched enough but I haven't found confirmation that putting the magazine follower from an S9 magazine into an S40 magazine yields a usable reliable 12 round 9 mm magazine for the S9. Anyone out there really done this with success? UPDATE! Thanks to Rebel49 the 9 mm and 40...
<p>Steyr S9-A1 10rd magazines (2). </p><p>Previously owned- tested and function. Purchased with gun + 7 mags. Previous owner had written in grease pen on side- mostly cleaned off.</p><p>This is for quantity of two 9mm, 10 rd magazines.</p>