Check to see that the grip screws aren't too tight, or that they still retain the lock washer. I had a similar issue with a P-220 that was issued to me, 13 years old at the time.
One night at work I said "what the heck" and decided to FULLY strip and clean the gun and inspect the main spring, hammer, etc. Somewhere along the line I dropped out the small lock washer on one screw and didn't notice. This made the screw set just enough deeper that the flat front of the screw was jamming up against the mag...too deep into the well.
Try backing out the screws a 1/2 turn (not too loose of course) and see if it helps.