In addition to our good Brother Dillinger's excellent job above regarding the assembly of the lower receiver and parts. I would like to add a technique for installation of the 6 position tactical stock.
While threading in the Extension Tube (Buffer Tube) into the Receiver the following technique will assist you with getting the proper engagement with the Buffer Retainer. While threading in the Extension Tube (Buffer Tube) assuring the Lock Nut (Castle Nut) and End Plate Adapter is completely to the rear on the Extension Tube (Buffer Tube). Hold down the Buffer Retainer compressing the Take Down Pin Spring at the rear of the Receiver and run the end of the Extension Tube (Buffer Tube) against the tip in the center of the Buffer Retainer. The stock will normally not be centered or straight at this point. Then back it off the Tip of the Buffer Retainer until the Stock is straight. And the toe of the stock is in line with the center mold mark on the back of the Pistol Grip. *Recommended! If the Extension Tube (Buffer Tube) contact point is less than 1/2 way between the outside edge of Buffer Retainer cylinder and the center Tip of the Buffer Retainer as recommended. It can be adjusted by taking a medium file and dressing off the raised surface of the end of the Extension Tube (Buffer Tube). If the tube is flat with no raised surface remove evenly all over. *Only about four of five light strokes with the file and then re-install and check the engagement of the Extension Tube (Buffer Tube) with the Tip and the outside edge of the Buffer Retainer. The point is! The closer the end of the Extension Tube is to the Tip of the Buffer Retainer and it still have clear movement up and down the better.
Failure to properly assemble the stock can result in a damaged receiver, since the Buffer Retainer without properly being positioned can result in the aluminum of the Receiver being pushed forward in front of the Buffer Retainer as the Buffer Retainer attempts to come out of position in the receiver as the buffer is pushing forward on it. In the case where you initially performing this technique and should the Stock be straight and the Extension Tube (Buffer Tube) be straight and slightly contacting the Tip on the Buffer Retainer. Attempt to tighten up the Lock Nut (Castle Nut) on the Extension Tube (Buffer Tube). A lot of the time this will square the Extension Tube (Buffer Tube) with the Receiver and the Buffer Retainer will move freely. *The point being the closer the Extension Tube (Buffer Tube) is to the Tip of the Buffer Retainer and it still have free movement the better! This will provide good strong positive retention of the Buffer as it comes forward.
* Once the End Plate Adapter is in position with the Stock. DO NOT MOVE THE STOCK FROM SIDE TO SIDE!!!! Be sure to lock down the Lock Nut (Castle Nut!)
Additional! When removing the Lock Nut (Castle Nut) from a rifle if not having a military stake on the end plate adapter. Be sure to heat the Lock Nut (Castle Nut) first. Rock River and other companies are using Thread Locker on them. Removing them without heating them first will result in damaging the threads on the Extension Tube (Buffer Tube).
Ronson makes a great small torch which is available from Wal-Mart, Lowes, Home Depot and other stores and refills with a Ronson Cigarette Lighter refill canister for under $30.00.