UPDATE - Magazine problem solved… I replaced the two plastic mag floor plates with the old steel ones, problem solved - mags seated fine. Not sure why or how because the other 8 mags I have with black plastic floor plates (all SW) worked fine in my 4586, 4506 and now the 645? As a side note I tried to talk with one of the gunsmiths at the SW Perf Center and no-go. As an old armorer when I was in the FBI (mostly revolvers), I could speak to them in Springfield when I needed to. Not any more apparently and the new folks at CS in Maryville, Tenn had no clue - I had some other questions about this 645 also. I'm afraid the old days of CS at SW are gone… unless you have a plastic pistol, an AR or one of their goofy lever action rifles… just my 2 pennies worth.