
that fit together, thusly.

Note the gate--this will limit your barrel length to 2 1/2" or so.

I only messed around with the plunger module, which looks like this when you open it.

Pull out the plunger, and you get this--sort of like a NF, but not identical.

The plunger on mine had a near-perfect seal out of the box; yours may require a little teflon tape under the o-ring. I added a 7/8" OD rubber washer to the plunger head, for padding:

Now, the tube. Grab the stock barrel (notice those holes in it?) and break it off; the end of the tube looks like this.

Saw that orange lip off, rip out the AR, and dremel the orange lip back until your barrel fits into it a bit. As has been discussed, you'll need to dremel this:

out until it looks like this.

Put a bead of hot glue around the orange lip, insert your 2-1/2" cpvc barrel, and add another bead of hot glue around the base. Make sure that the barrel ends up straight. Hot glue will work for this, as the barrel is almost entirely recessed. Here's the tube with the new barrel.

Reassemble and close up the module.

I wasn't able to find a spring combo I liked, so I just added a couple of fairly stout rubber bands. Here's the finished product:
BeNERFstronged

Primed

Front

Sight view. That's right; it has sights.

Ranges: Don't know, don't really care. Plenty to qualify this as my new sidearm.