Do you know the condition of the mag springs? I ask because Wolff extra power mag springs can cause the slide to lock open on the last round during the break in period. I would load up the mags and let them sit for a week and retry or borrow someone elses mags that they know work. At the very least you can determine if it is the mags or the gun.

I'm with FILO on this.

Sir, I know you have WAY more experience with firearms than I but have you checked to make sure the nose of the rounds are not moving in the magzine and inadverantly hitting the slide lock lever?

(Its the only thing I can think of without consulting my armor's manual)

Do the mags in question have a "U-shaped" or rectangular notch in the back?

If its a "U-shape", some of the newer followers for the .40 S&W magazines ride higher in the nose than the older followers. I had a pair of the 1st gen mags for my Glock 35, and one of them does the exact same thing with the new followers, and one does not.

The "U-shaped" notched mags are all 1st generation, NFML. They only have metal on three sides of the magazine.

Ralph Arredondo (www.arredondoaccessories.com) makes a follower for the Glock .40 mags that work really well with aftermarket springs. I never tried one in the NFML variety mags.

I have a contact with Glock who has a large collection of older parts, and I might be able to scare up some older followers to see if they will work, or you could just get some new full caps for about $20 or so by EOM October.

Apparently I am jumping into this thread a bit late but so be it.

If I came up with a G17 for free I'd keep it. I highly doubt I would spend my own money on one though.

I had one of the early Glock .40 S&W's. I had three malfunctions during a qual shoot and went back to my Colt .45. I think I just had a lemon. Still, as an old team mate used to say "Steel is real!" If I'm going to carry plastic, I'll go with the H&K USP compact in .40 or .45. I carried one for several years and it was great. Whatever you decide to buy, go with the .40 or .45 and stay away from the .380 magnum (aka 9mm).