OK, I'm an AR newbie. After doing some work on my stock, the pin that holds the lower and upper together falls out. Not the pivot pin on the muzzle end, the pin by the buffer tube. What can be done other than putting a piece of duct tape on it to hold it?

There's got to be an easy solution...

Thanks!

What did you do to the stock? Did you remove the castle nut and end plate? Some how you have lost the detent that is held in place by the end plate and keeps the rear takedown pin in place.

Thanks! I changed out the buffer tube, going to an adjustable stock. Thought the buffer tube retainer was the only thing that needed to be held in place with the buffer tube screwed in just far enough. So, what am I watching for with the buffer tube and castle nut?

Video shows it. At about 0:56 in the vid you will see the pin that is held by the stock. The person in the vid also makes mention of it.

http://www.brownells.com/.aspx/lid=1...To_Collapsible

Take a look at this vid... fast forward to about the 8:20 min mark where he is installing the buffer tube. The video will show the detent and spring that you install in the rear of the receiver to hold in the takedown pin.

Thanks! Never saw the detent and the spring. Was too occupied with the buffer retention. Now I just need to find a replacement pin and spring.

Brownell's, MidwayUSA, even contact S&W and they might just send you a new one.