Here is my second concept so far, and it is a very cool one. It's a Double action Nerf Pistol, based on the M1911, which can use either stefans, or rival ammo.
This is a rough layout of the mechanics, but it's still very simple. The entire system can be seen in Fig. 8 and 9. It uses the same mechanism as in a Automatic center punch, A tool used in metalwork (fig 6). This works by having a block under spring tension, so that the plunger cannot move. When the block is moved in line with the plunger, it fires the whole mechanism. This allows for more powerful springs, and therefore, more power behind the dart. The system can be cocked either by a trigger pull, or by pulling back on the lower nobs as seen on the bottom of the plunger cylinder. Loading is done by having the barrel move back and forth.
Currently, I am working on adding a Saftey, Hammer, magazine port, and other features.
Again, this is still a work in progress, but if there are any suggestions, and/or critiques, please leave them down below.