M P 40 mag drops under recoil

[jobbass]

M&P 40 full size Gen 1, I had this for few years, never had any issue, today at the range , after few rounds, with no issue, mag start dropping after each shot.
I changed my hand position, checked the spring , looked for cracks, I have no clue what suddenly is happening.

Any inputs.

 

[alpining]

You're absolutely sure that it's not your grip? Same issue when shooting with your weak hand? Or when another shooter uses it?

After the magazine is properly seated, can you pull the magazine out by main force?

If those all come up negative, I'd do a complete disassembly and cleaning of the frame around the mag release. There could be debris or fouling slowing down the mag release spring.