Dead Foot Arms has introduced an AR-15 buffer tube with a quick stock deployment feature. In order to extend the stock, you simply need to pull it back. The stock will extend and stop at a preset length. Then, collapsing it back is accomplished by pressing the lever just like in the case of conventional AR-15 stocks and buffer tubes. You can see how that works in the video below.
This system works due to ratchet teeth machined into the bottom portion of the AR-15 buffer tube (see the top image). In conventional buffer tubes, there are blind holes machined into this area to let the stock lock in different positions. In the case of Dead Foot Arms buffer tube, it is a simple ratchet mechanism which allows a linear movement in one direction (rearward) and prevents it in the opposite direction (forward).
Note also that each ratchet tooth has a tapped hole. Once you choose the length of stock that works best for you, then you will need to install (screw in) a pin into the corresponding hole thus making a stopping point for the stock. Once this stop point is set, the stock can’t be adjusted to a longer length of pull than that. At first, it may seem to be a limitation. However, the idea behind this system is to deploy the stock as quickly as possible to the position (length) you mostly use. Many people will agree that there is one length of the stock that fits them perfectly. Many shooters don’t use the multiple positions, but rather fully collapse it and extended to that single position. If that is how you use your adjustable stock, then maybe this product will be valuable for you.