Guys; first off, another .40 jamming thread. I am beginning to believe the .40 has more issues in all makes and models than any other cartridge.
Your jamming issues sound similar to those I had with a Glock 10mm and heavy loads. Glock and I finally figured it was caused by a stiff hold and slide speed exceeding the ability of all magazine springs to align a round in place before the slide arrived to strip the next round, thus producing slide overrides. Investigation on my part indicated a fairly rare but recurring problem with others who shot heavy loads in their G20's. The gun was a total lemon and Glock was very helpful all the way thru the testing, etc. They eventually took the gun back.
No problems with ".40-power" loads, by the way.
Your situation could be different, but I give you mine for what it's worth. Maybe nothing.
I've not heard of this problem with 320's, but your assessment in this case seems entirely plausible. I've not heard of magazine problems with 320's in this caliber, but who know.
I have 4 P250's and have had no problems with any of them other than their insatiable appetite for ammo. Zero problems with "pointed" rounds like XTP's and HAP's and the old Fiocchi Extremas. All are 9mm's. I also have a .45 P250 that like our old P220's feeds anything except LSWC's that have the bullet shoulder seated to the case mouth.
Good luck. I know problems like yours can be really frustrating.