NOTE: THIS VERSION HAS BE REPORTED NOT TO WORK. I AM WORKING TO UPDATE AND IMPROVE THE PERFORMANCE OF THIS BARREL.
Note, these are only useful for high performance, modded blasters that shoot above about 150 ft/s. This barrel has a 100mm long rifled section with 1:4 rifling. Not sure how the fit will be with all darts but should be close to good. Ported version are probably going to help some with air blasters with excess compressed gas to reduce back blast but dunno how much of a real difference it would make.
16mm should work for 16mm electrical conduit, Artifact barrels, and 1/2in thinwall PVC.
If you print one please let me know how it works for your blaster! Suggested not to use support