Summary

A double barreled nerf blowgun with a 24 dart capacity. Identical in function to the Plusblow 5, but uses the more common Nerf Elite / Streamline darts.

See the video here: https://www.youtube.com/watch?v=frRRKE2z8Ak

Instructions

Print 1 each of the .stl files. You may need to adjust the hole fit for your individual printer--a .stp file is provided for those that have a CAD system to edit the parts.
Cut 4 pieces of 9/16" ID, 5/8" OD plastic tube to equal lengths. I got mine from McMaster #8628K57 . I used 30" to get the 24 dart capacity and to best use the 5 foot long segments of tube.
File the top of the dart holder drum so it's smooth enough to superglue, then glue that surface to the bottom of the mouthpiece, lining up the holes as best you can.
Drill out the center hole to 1/4" as needed, then put a 6" long 1/4-20 screw through the mouthpiece, dart holder drum, and the magazine holder drum. The smooth bottom surfaces of the dart holder drum and the magazine holder drum should be pressed against each other. The head of the screw should be on the mouthpiece side.
Put a 1/4-20 nut loosely on the screw. Tighten it down so that the dart holder drum and magazine holder drum are gently pressed against each other.
Put a dab of superglue just above the nut from step 6, then put another 1/4-20 nut on the screw. Tighten the nuts against each other, but not against the printed parts. At the end of this step, the magazine holder drum should be pressed against the rest of the assembly, but not so hard that it's difficult to turn.
Insert the four 9/16" x 5/8" plastic tubes.
Place the front magazine holder on the barrels/magazines at the front of the blowgun. Press everything together.
Add a strip of rubber or other flexible material in the provided slot to create a dart-retaining flap. I hot-glued a couple strips of rubber in there, but you could achieve the same effect with cardboard or folded paper if need be.
Put some orange tape on the tip of this to prevent anyone from getting butthurt about toy gun ID.

To load the magazines, push darts past the flaps into the thinwall PVC magazines. With this length, you should be able to fit 11 into each of the two magazine tubes. To load darts into the firing chambers/ barrels, just tilt back and rotate the mouthpiece/dart holder drum 90 degrees. To fire, just blow each of the two mouthpiece holes in front of the barrels.

Accuracy will suffer greatly compared to the Plusblow 5 unless elite suction darts are used, because regular elite darts don't fly straight.

Plusblow 5N