This is a drop-in replacement barrel end-cap of the Dart Zone Pro Mk 4 blaster extended barrel. Open three screws, pull out the old cap mount and barrel, drop in the new cap, and close it up. Now you can use any length barrel you like ( I recycled one pulled from a Zuru Longshot ) and fix it in place with a 016 o-ring and the Sillybutts collet nub of your choice. I like the on in this remix.
Remix portion of this blaster derives the threading from Sillybutt's Talonclaw work.
The author remixed this model.