I made a 3D-printable replacement cylinder for the HammerShot that fits standard 1/2" PETG!
It uses the existing ratchet mechanism and requires no dicking around with the seal. Ranges are 30-60 feet with my ancient Slugs, but better darts will probably fly further. This is a really fun blaster and makes a great sidearm.
Because I can't attach the STL file or the SketchUp CAD file here, I hosted the files on Thingiverse. You can download the STL and editable CAD file, and read the installation instructions, at http://www.thingiverse.com/thing:1621677 .
What?! Zack the Mack?!