As wonderful as Buzbee shells are, they're a bit lackluster when it comes to performance. Of course, you could drill, sand & brass the original shells or opt for printing them for a bit less fps, but I didn't do that. Instead, I went for a mix of both with simplicity & performance in mind. Print the shells then cut the brass and glue it together, simple as 1-2-3!  

For tools, you'll need; pipe cutter, sandpaper, and deburring tool (optional but recommended) 

Once you printed the shells you need a 13.49mm brass tube, you can get this from your average Ace hardware or Home Depot. After you cut it I recommend sanding and deburring the edges to remove the excess material as it will cut up your darts and cause drag if you don't. I cut mine to 47mm-ish to make it compatible with Gemeneye's Buzz Bee Shell Magazines found Here.  

I haven't fully tested it so pls leave comments if you have any ideas on how to improve the design. Peace!