3rd Gen .40cal Magazines - Changes to feed lips?

[Haybinger]

So a few years back I acquired a non-S&W gun that was designed around 3rd-gen S&W magazines. The gun came with one 4006(?) magazine and one modified Mod 39 mag. The gun was designed in the late 80s/early 90s which appears to be some point before changes were made to these mags (perhaps brought on by the '94 AWB?).

I never really bothered getting more magazines for a while as the gun was mostly a curiousity. Eventually though I ended up happening upon a 4006 magazine for cheap. After getting it home it did not fit in my gun - there is no notch for the front mag nub to run up in despite the gun being .40cal. Easy fix with a bit of sanding.

The real problem came in that the breech face of the slide is not able to pass through the feed lips of the mag. The original mag that came with the gun has a deeper, rounded cut-out whereas this mag has a flat and shallow feed lip cut. But on further investigation almost every single 3rd-gen .40cal mag I have seen since has this smaller cutout. Can anyone tell me when/why this change was made, and what magazines I should actually be looking for?

I have attached photos to show what I mean, yellow follower mag came with the gun, orange follower is the modified mag and the blue follower is the one I got after the fact.

 

[snw19_357]

...a non-S&W gun that was designed around 3rd-gen S&W magazines...The original mag that came with the gun has a deeper, rounded cut-out whereas this mag has a flat and shallow feed lip cut...yellow follower mag came with the gun, orange follower is the modified mag...

(orange is a modified 10 round 59xx mag)

Looks like they modified the yellow follower magazine to work in your non S&W. ALL my 40xx and 59xx magazines are like the one with the blue follower.