Some do not realize the importance of proper installation of the collapsible stock. This Thread will cover the six position collapsible stock although others install the same.
Improper installation of the collapsible stock can cause serious operational problems with the weapon as well as "Trash The Receiver. In this thread we will refer to the distance between the front of the Extension Tube (Buffer Tub) (Threaded End) and the Tip on top of the Buffer Retainer as "Engagement!" *Critical Point! If the Extension Tube is not in the proper position to hold and maintain the Buffer Retainer in position while the weapon is firing, the weapon can stop operating and serious damage can happen to the Receiver. This occurs when the Buffer Retainer starts working and coming out of the Receiver in front of the Extension Tube due to improper installation. As it begins to come out it starts coming out at an angle, since at the same time the Buffer powered by the Buffer Spring is slamming into it as it works out. This can cause the aluminum on the Receiver in front of the Buffer Retainer to crack and begin to tear out as the Buffer Retainer comes out. In several cases the Receiver is damaged to the point of no repair only replacement.
Many AR weapons I have observed do not have proper Engagement.
So what is proper Engagement? Proper Engagement should be that the front edge of the Extension Tube (Buffer Tube) is in position 1/2 way between the outside cylinder wall of the Buffer Retainer and the Tip of the Buffer Retainer.
In this case the closer to the Tip of the Buffer Retainer is the better, as long as the Buffer Retainer moves up and down freely. The following instructions will assure you of maximum engagement with out the thought of "Could I have turned it in one more turn? I have seen many ARs that the person put a collapsible stock on and should have turned the Extension Tube one more turn in. So to eliminate the guessing, the following is the method I use in the schools step by step.
1. Insert the Buffer Retainer and Spring into position in the Receiver
2. Be sure the Castle (Lock) Nut and End Plate Adapter are all the way to the
rear of the of the Extension Tube and loose! This will eliminate Stock
movement when you are tightening them later!
3. Insert the the Take Down Pin, Detent & Spring *If installed-
4. Assure that the Take Down Pin Detent is in the Track on the Take Down
Pin. *Use caution not to hit the spring while completing the stock
5. Begin screwing the Extension Tube into the Receiver (Clockwise)
6. As soon as the Extension Tube starts to make contact with the Buffer
Retainer, depress the Buffer Retainer and continue to turn the Extension
Tube (Buffer Tube) into the Receiver until the *Front of the Extension
Tube makes contact with the Tip on top of the Buffer Retainer.
7. Then "Only" back the Stock Off (counter clockwise) until the Stock is
Check the Engagement at this point for correct position. *See the
section on adjustment below if not correct! If Correct continue.
8. Push the End Plate forward into place using caution not to damage the
Take Down Pin Spring (No. 1 Most damaged part on the rifle)
9. While Holding the End Plate Adapter in place against the rear of the
Receiver tighten the Castle Nut (Lock Nut)against the End Plate Adapter
using caution not to turn the Stock once the End Plat is into position on
the Receiver. Doing so will cut the threads off the Extension Tube caused
by the End Plate Adapter's solid Locator Pin
Should you experience a situation where the Engagement is less than suggested, With the *Correct position being with the Extension Tube being 1/2 way or closer on the Buffer Retainer Tip. You can adjust it by taking the Extension Tube back off the Receiver. Most quality Extension Tubes today have what I call a raised (Cam) surface on the bottom edge. In the case of not enough Engagement as mentioned, you can take a medium file and dress off some of this raised (Cam) surface. Do it in small increments taking very little metal off and then check it after each process. It will take very little filing to allow proper Engagement of the Buffer Retainer and the Extension Tube.
If it is an Extension Tube that is flat all the way across. You will need to file the entire end of the Extension Tube or you can Notch the Tube over the Buffer Retainer which I do not prefer.