[tsimanson]

First off, I am new to AR rifles. I bought the M&P 15 sport 5.56 and haven't even fired it yet. The buffer retention pin fell out and logged itself between the hammer and the lower frame. I removed the hammer to get the pin out and reinstalled both. After a few dry cycles the pin and spring fell out again and jammed up. Any idea why this is happening. I plan on taking it back to to store under the protection plan I purchased to have it fixed but was curious since so many people rate it as a good, reliable rifle. I don't want to fire it before they fix it and risk blowing it up. The only thing I have done otherwise was adding a single point sling plate.

 

[series guy]

It sounds like your buffer tube isn't screwed into the lower far enough. This would mean that the buffer is holding the plunger in place. As soon as the bolt cycles and pushes the buffer rearward the plunger can jump up into the bolt and get carried into the action. A pretty minor adjustment.

 

[Injunbro]

Did the single point sling plate you added change the fit of the buffer tube to the lower? If so you may have created the issue series guy posted. Sounds like a little minor tinkering could fix it.