9mm STI 140mm mag nightmares, HELP!

[cheers623]

My wife and I have been shooting USPSA for years. Been using my various STI .40 cal 2011s with no problems ever. I've tuned maybe 14-18 140mm magazines using the Dawson vids and tools, various spring and follower combos, and lots of different basepads. All with good effect and reliability as long as the ammo and gun were setup correctly.

HOWEVER....I finally purchased a dedicated Limited gun to be my wife's. An STI Tactical in 9mm...there's the problem. The gun is fine, extractor tuned, ejection fine, feed ramp polished blended, chamber polished, breech face good to go, etc. It runs with no problems with the 126mm mags. BUT, with the 140mm mags loaded more than 17-18 rounds it has a nosedive failure to feed from the top round EVERYTIME. Dawson 9mm basepads, STI 9mm factory followers de-burred, 140mm STI springs, and polished/de-burred STI spacers. I've even tried the Hardy steel spacers. Same problem.

Now, the load is not helping possibly. Her favorite load is Rainier 124gr hollowpoints, over Ramshot Competition, with COAL of 1.135". We've tried loading both longer and shorter and still get the exact same problem. So my question is...what can I do? Should we give up on the hollowpoints entirely and start with round nose profile? I'm skeptical because the nosedive is so pronounced I think it'll have the same problem regardless. Different followers, springs, etc? Any mag tuning gurus that specialize in 9mm 140 length mags? Most folks that shoot 9major use round nose bullets around here. I've tried bending the spring, 1 coil after the follower to add a nose-up bias on the springs...no luck. It just seems like the tapered wall cases curve too much after around 17-18 rounds in the mags. The mags will hold 21 rounds but never work with more than 17-18 in them. My wife is really disappointed. Any help is GREATLY appreciated.

Cheers623

DVC