I started to brainstorm then.
I had some non-leaky Hornet barrels, a Big Salvo pump, and a fuckton of assorted parts from broken guns. I eventually settled on my AT3K, from which I then harvested the handle and the trigger. Here's the result of some hour or so of work:

It's, um, really strange. To get a sense of scale, it's almost identical in length to the Maverick with the pump in, and slightly shorter and narrower. I had to cut open the Big Salvo pump to situate the AT3K trigger, so while it was open I plugged it, which primes the gun really quickly since Hornet barrels are miniscule. I plugged the last two holes since that AT3K trigger pull is only long enough to actuate the first two blasts.

I cut apart the Big Salvo trigger mechanism and gooped it together, and then put some hot glue around the joint. After that I epoxy puttied the rod to the AT3K trigger. Visible here are the circles of electrical tape I wrapped around the Big Salvo pump so it would sit tighter inside the AT3K trigger.

Same thing, this is just the trigger depressed all the way.

To prevent air leak I plugged the last two holes on the Big Salvo pump with hot glue. It should keep it sealed.

Here's the front of the gun. I haven't glued down the Hornet blast chambers (they're held there with Gorilla Tape for the moment) but they've been couplered. I've found that the easiest way to de-restrict airflow in Hornet valves is cut exactly where the white part of the tank ends. That's the point where the white cover Ompa's mod has you pull out with pliers ends; once you cut it's trivial to just pull off. For the barrels I use six inches of PVC with about three inches of CPVC nested inside (I had to dremel out the inside of the PVC for it to fit).
I don't really feel the need to explain in step-by-step detail the process for making one of these. The gun is nearly stark naked and the internals are pretty easy to figure out. Instead, I'll skip that and get right to the point everyone wants to know: ranges.
Using slightly tight darts, fired in a moderately warm, dry hallway, at four pumps, the first barrel reached:
67
72
69
70
69
The second barrel, same conditions, same darts, reached:
65
69
70
64
62
Trigger pull on the AT3K gets a little sticky farther back, so I imagine the slight decrease in range is due to the valve not being opened as quickly as it should.
All in all, this is a fucking insane sidearm. Eventually, I hope to turret one of the barrels for slightly higher ROF but I'll keep at least one coupler-loading, since it's not a terribly slow system.
Edited by Ice Nine, 05 January 2009 - 06:36 PM.