I got more PETG yesterday, so here is my promised write-up. The first step is obviously to pry off the back of the clip. This is glued on, to it's a bit of a pain. Just take it slow and be careful, and it will come off without trouble.
Once you've got this piece off, pry out the air restrictor washers. It will look like this now:
Now mark the clip where you want to cut those wing things off. I used a bandsaw to cut them and also the old barrels. I cut 1/8" or so out, then cleaned up the cuts on my mill. A dremel would do the job just fine.
Now comes the drilling. First, drill all the barrels through with a 9/16" bit. At first I though I could just press the PETG into these holes, but they are too tight. I destroyed 3 pieces of PETG trying. Instead, use a 5/8" bit to drill about 3/4 of the way down, leaving a 1/2" or so at the back that is still 9/16" diameter.
Those holes are still a little too tight for the tube, so switch back to the 9/16" bit and run it through again, wiggling the clip to ream out the holes slightly larger. That takes care of the clip body, now just cut your PETG to length. I used 3" long barrels, which are the longest you can fit in the Mag's slot. If you want to be able to fire stock darts, make them a bit shorter. Now press them in one at a time, using a vise.
The back end should look like this:
All that's left is to glue the back piece back on. I used epoxy. Goop it all over the back, but be careful not to get too much into the tubing. Once I put the back on, I set it up on a couple blocks and piled some steel on it while it dried.
That's it! The new clip should fire about 10 feet further now.
