The recoil spring needed to be ground off. No problem with that. While i was at it, i polished the feed ramp on my P64 as well. I then tried hand feeding the HPs (slowly) without a hitch in all 3 mags (slide locked open).
So i took it to the range yesterday to try it out. I have 2 mags of HP and a mag of FMJ. My friend then tried 2 more mags of the FMJ. Here are the results:
1. The recoil improved, though it's still annoying to my friend (first timer).
2. Issue: All mags ran ok EXCEPT on the last mag of one of the HP where the last shot the slide didn't lock. BUT loading the same mag with FMJ didn't have that problem. In fact my friend shot the last 2 mags of FMJ.
3. Fiocchi FMJ is more accurate than Silver Bear FMJ. Silver Bear HP is very satisfactory.
4. I looove my P64

Overall I am glad the HP worked as in the future, this will be my carry gun.
I think polishing the ramp with heavier recoil spring help with that.