This thing is used to grip the Nerf barrel extension port on some Nerf guns and couple it to a piece of 1/2in PVC. The scad file in the src.zip file allows you to change the diameter of the pipe if you find your local supplier is of a slightly different size.
With the release of the new line of nerf guns the older models have gone on clearance at many retailers. The pictured Rayven was more than 2/3 off MSRP at walmart. Although they may no longer be up to snuff compared to the newer models stock they contain at least their cost in parts for modding.
Since this is a flywheel based blaster it is trivial to run it at higher RPM for more range. Unfortunately this make it considerably less accurate. As per common wisdom one can theoretically compensate for this with a longer barrel. Nerf does not sell barrel extension pieces separately so this is a quick trial piece.
Quick unscientific testing shows that this gets ranges better then my newer Nerf guns and has comparable accuracy. It does seem to also make the gun more picky about which darts it will fire. Of course I plan to trim the barrel extension and paint it orange to comply with local laws but it's picture this way for maximum ridiculousness.
The src.zip file contains the scad script for generating the piece, the dxf file that corresponds to the locking mechanism, and the sketchup file used to draw the dxf.
I added a modified version for use with a thinner walled pipe. The older version uses pvc with an outer diameter of 21.5mm and the newer one uses a tube with an OD of 18.5 mm. This allows it to nest further into the barrel and fire warped darts better since it reduces the internal ridge. The newer tube I'm using is 1/2in steel electrical conduit.
If printed from the posted STL you will need to snap off the bottom cm or so of the inner ring once it's done. This bit conflicts with the tip of the barrel from most Nerf guns. It's included here so that the inner tube that grips the barrel can be printed longer and grip the PVC pipe better (guarantee straight barrel). The scad file contains a mechanism to remove this before printing if desired.
You will need a 1/2 in pvc pipe. Note that this needs to be a loose fit on the nerf darts. Not all PVC pipe is the same size despite listings. Compare inner diameter to the inside of the existing barrel and then set the outer diameter in the scad if needed.