This is a short instruction on how to build an aluminium Coldsteel-style big bore blowgun, shown here on the left (next to the 11mm blowgun).
The blowgun is made from 16x19mm seamless, round aluminium tube, 1500mm long (bought here).
It is suitable for use with Coldsteel big bore blowgun darts with 5/8" (15.875) diameter.
The blowgun has a protection against inhaling the dart and a magnetic dart retention system.
The material for this blowgun costs less than €10, not including the darts.
The mouthpiece is made from a 30mm length of round 100mm PVC tube. Or in my case, from two 30mm lengths of round 50mm PVC tube which was what I have in stock. Saw both 30mm rings in half, leaving you with 4 pieces of PVC, measuring ~78mm x 30mm. Here are the pieces shown next to a blowgun 'I prepared earlier'.
Heat three of the PVC pieces and form them on a 100mm round form, so they fit together seamless without stress. I Used a hot air blower to heat the PVC. Be careful not to melt your workbench ;-)
Next, glue the pieces together with PVC glue, clamp and let dry.
Form the mouthpiece using a Dremel (or in my case, a "Ferm"). Leave a 20mm x 20mm area in the center the full thickness, this is where the aluminium tube will be glued in. Taper the mouthpiece towards both ends. Do not machine the mouth side of the mouthpiece.
Drill a 19mm hole in the mouthpiece using a speed drill. Don't drill all the way through, leave ~2mm of material on the 'mouth' side of the mouthpiece.
Ream the hole to 15.8mm (approximately) from the other side using a tapered reamer. Stop reaming when the dart cone just barely fits through the hole. This way, the mouthpiece will act as a protection device, to prevent you inhaling the dart.
De-burr both sides of the aluminium tube and chamfer the inner and outer diameter. Fit the tube to the mouthpiece and make sure that the dart feeds through the mouthpiece into the tube.
Use epoxy (5 Minute Araldite) to fix the mouthpiece to the aluminium tube and let dry.
Determine the correct place for the rare-earth magnet as shown below.
Wrap ~200mm with ~3.5m Paracord in a color of your liking. Wrap of the magnet to fix it in place. Loop the end of the paracord onder the last 5 wraps. Cut and melt the cord to fix in place. The magnet will hold the (metal) dart in place when the blowgun is aimed down.
And here is the end-result. On the left, the big-bore blowgun for 16mm mini broadhead darts, and for comparison a 1200mm blowgun for 10mm needle-darts on the right.
And now, enjoy!