Ran a Steel Challenge 5-stage match with the 9mm Colt today. Functioned perfectly with one specific ammunition.
Yes, this is what it took to get the ejection to run properly. Winchester M1152. (These numbers were confirmed with a LabRadar unit running at the same time, so yes those are real- this is very nearly 9mm Major.)
That tells me all I need to know about the spring rate in this thing.
Obviously I'm installing a proper GI guide rod and a 10# IMSI spring tomorrow. That should make it a bit more tolerant of more normal 9mm ammo.