I've got a friend still in Denver who has a Shield in 40 that he says has excessive recoil. I'm not sure when he bought it but I told him to swap with his 9mm guns to see if the recoil spring assembly was defective.

Do they both have the same recoil spring assembly? If not I'll text him and tell him to hold off and just buy a new assembly for the 40.

I just shot a few rounds of 40 out of a Shield yesterday, I don't think it was excessive considering the smaller frame and my first pistol was a 40 so I am not phased by the "recoil concerns with 40"

The 40 has a very snappy recoil pulse. The 9mm is mild, the 45 is like a gentle push, the 40 slaps. That's why the 40 is being replaced in the field by the 9mm. Some found it too snappy for good accuracy.