Followup failure to feed
To follow up on an earlier post about failure to feed in a SP9A3G with 33rd mags, I got three of the high power springs from HBI. I put one in a SGM mag the gun came with, one in a glock oem mag, and one in a KCI mag.
All of them had LRBHO now. However, the Glock mag still had the worst performance. It would still exhibit the same ftf issue, although with a bit less frequency. SGM was a bit better in this regard. The real winner was KCI. No failures of any kind, achieved LRBHO consistently, even mag dumped it from completely full and it just kept working.
I'll note that I think the HBI springs are probably required for any 33rd mag and it really narrows down to the top few rounds having feed problems. I'd put a reliability ceiling at 30 rounds loaded unless you've had a bunch of rounds through a specific mag with no issues. 30 and under you'll probably be okay. It was weird the KCI one was the one that worked without issue because they get a bad rap. This is anecdotal and not a comprehensive scientific analysis, so YMMV. The real root of the problem is probably the turbo ass feed ramp though.
Honorable mention to the Magpul 28rd pmag. You won't get LRBHO but those also just seem to work.