I field stripped my MP 12 to give it a once over before taking to the range for the first time. Upon reassembly, I had to remove the upper again as I felt some resistance, I did not use any force once I notice this. After removing the upper a very small retaining ring/clip that is open on one side fell out. I have no idea where it goes or how it was knocked loose. It’s not in the owner’s manual and cannot find any field strip videos that reference it. Any help would be appreciated! (photo attached) I think it goes on the trigger pin?
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