This is an experimental air stripper for Nerf-type foam blasters. The idea is that this is fitted over the muzzle of a blaster, and the ports will strip away excess air as the dart exits the muzzle. The theory is that the sudden exit of excess air will disturb the dart and will affect its trajectory leading to inaccurate shots.
I made mine to fit over a 9/16" brass barrel, but the included scad file will allow it to be customized to almost anything. You could also use the makerbot customizer to edit the parameters and generate a custom model. Click the "view source" button to see the parameter descriptions.
More testing is required to tune this for optimal effect (port sizes, cone dimensions, barrel insertion depth), but initial tests indicate that full length darts fly much straighter with less fish tailing/spiraling.
I printed mine at 50% infill but lower infills will probably work ok too, if you don't have to wrench on it to get it slip over the barrel.