Alexlebrit

I've actually built one of these, but using BB's not darts (shhhhhh) and unregulated CO2. For spehrical hard ammunition it works great, the rotatling breech also acts as your firing valve as your projectile can only be fired when the breech is fully open. Prior to that it's blocked from moving and so no air escapes. As a BB Machine gun it's very effecient, and of course you can adjust the rate of fire with a speed controller.

HOWEVER. I'm not using any form of cartridge so don't need to eject anything, I'm using small, round hard ammo. I'm not totally certain you could get this to work simply with a cartridge as there's a very strong risk of jamming on the loading or ejection cycles. Don't forget even the HK is caseless.

On the subjest of lubbing the plunger head, can I recommend KY-Jelly or similar. Ok so you've got to go into the pharmacy and ask for a syringe and some water-based lubricant jelly, and this might get you some funny looks (ask for condoms while you're in there, get all the embarressment over in one go), but it really works as a syringe lube, and won't cause any plunger head damage.

In general I'd say I was anti-plans too, could I suggest instead you give the full post on Spudtech a good read, and if you've got sensible questions to ask them there? Like I said I had no hand at all in this thing, I just saw it on Spudtech and thought that you guys might be able to think use it as a basis for a nerf belt fed gun. I doubt there'll ever be plans for it though as Plow has said it's still in development. But who knows perhaps someone here wil take it to the next level?

To do the 3 plates for the ebay guns I cut them out on the band saw my father has.  Definitiely the quickest way.  I used a Dremel before because it's all I have at my apartment.  It was worth the trip to for 3 to save the time. 

You probably could do it with a hacksaw and a vise.  To do the slot you could just drill a lin of holes and file out whats left over.

Is there any reason not to use brass for this component? The great thing about brass is that it's soft to work with, and because it's self lubricating your saws, drills and files don't jam as much as aluminium or steel.

The other advantage of brass sliding inside brass is that it's self lubricating, which means you can get much greater tolerances and avoid jams. This in turn makes sealing things easier.

Don't be scared of brass it's a lovely material to work with, and because it's quite soft you can use hand tools a lot of the time.