Ways to Protect Mosfet from Burning on PWM for running universal dc motor?
I'd suggest your problem is nothing to do with inrush current.
You have no protection for the G20N50C, and are driving a highly inductive load.
Put commutation protection across the motor:

 

What is the driving PWM schematic? I hope the R4_1G is not in any way defining the turn on charge timing for the G20N50C gate. For applications such as you have you need very fast gate charge and discharge times.