When you installed the new stock, you did not screw the receiver extension far enough into the receiver to retain the buffer detent pin*, or you had a primer blow and is now stuck somewhere in the action.

If trying to get the bolt back closed so you can shotgun the receivers apart is not a option**, you will need to pull the receiver extension from the rifle (leave the upper and lower together). With the stock assembly off the lower receiver, you may luck out and find that instead of the blown primer/ buffer retainer pin in the buffer tube, the part is wedged in between the carrier and some part of the upper receiver.  Since you have the back of the receiver open, you should be able to see/find the wedge piece to free the action.

* When a carbine receiver extension is installed, the tube is threaded into the receiver (with the buffer retaining pin held down) until the edge of the tube contacts the middle post of the buffer retainer.  From that point, the tube is back threaded the needed amount to index it correctly for the stock.  At this point, you double check the edge of the tube to confirm that it does still enough contact of the barring flat of the buffer retaining pin to hold it in place.  If the tube overhang on the flat is in question, then the end of the tube will need to be shortened to allow it to be threaded in one more turn to correctly index it for the butt stock, and still retain the buffer retaining pin (read you want the end of the tube to kiss the center post of the buffer retaining pin when correctly indexed for the stock).



**See if you can bump the muzzle of the rifle off the carpet while pushing in on the forward assist to walk the bolt closed.  With the bolt closed, you can shotgun the receivers apart and find the wedged piece.

Quoted: FIXED!!!!! Thanks for the help! The culprits! i129.photobucket.com/albums/p207/duckhoward/DSC06646Small.jpg

Not quite yet, you need to pull the FCG and check under the trigger, with my guess, the anvil sections of the blown primers hiding there.