I did some mods to my M&P 10 a few weeks Ago and finally got out to the range to test it out. After the first magazine I put through it I noticed that the ejection port cover pin had backed itself or in the M&P 10s case forwarded itself out. My question is is there a c clip on the pin if so mine is not there and I can't find a groove on the pin anywhere.
Well , I just looked at mine and I do not see any clip. My pin will move back and forth , but will not come out because the front stops at what I believe is the barrel nut. Hope that helps.
im glad i ran across this thread. i had the same type of problem happen to me, kind of... When i opened mine up brand new and got it out of the box i noticed that the rod was up against the barrel nut. i didnt pay it much attention until a friend was looking at it and noticed that the ejection port door was very tight and would barely open. i got a hard plastic wedge and finally got it to snap back into place. but mine came from the factory that way. i didnt see any type of clip or anything so im not sure if it will back out again or not.... time will tell