I've wondered if sprockets are the best way, or if a proper pawl setup would be better and NERF et. al. doesn't do it because they're used to turrets and turrets work fine for stock blasters.
Either way, I was thinking 1" 200 PSI PVC would be a good shell size. 3 darts should fit no problem, 4 if you cram them in, mega/rivals could also fit if you wanted. OD is 1.315" for all varieties of 1" PVC, ID is +/- 1.16-1.189". PVC because it'd be cheap enough to build a belt out of: 10' of the stuff would make ~40 links in the chain for ~$5 (plus whatever filler you use to make the barrels). When I was considering it more seriously, I was going to make a jig to just duct tape the shells together into a belt. Seemed like a good combination of simple, reliable, and cheap.
Oh wow, I misunderstood what you were asking for. For some reason I got in my head that you wanted to chain feed a doomsayer. So what you are asking for is a chain fed shotgun in the literal sense. That's a bit different than what I had in my head. Let me think for a bit on that.
Again, rifling isn't really what matters here. Check out Slug's recent thread about the VF1 barrel alongside the SCAR. Both were identical unless the fit wasn't right in the SCAR, then performance was better on the SCAR. The whole idea of fishing line is an adjustable elastic barrel, not to impart spin. People like JSPB and others who do it for spin are correlating two things and assuming causation. In terms of fluid dyanmics, it makes no sense that spin would help a nerf dart, DOOM wrote a dissertation-style nerf document that modeled a dart and came to the same conclusion, and cited evidence that spin doesn't help. DOOM'd document is an excellent read if you're up for it, its on his website, go read it.
What Meaker is getting at is there is zero advantage to turning/milling a rifled barrel for nerf. Either 3D print Slug's VF1 and tune the diameter, or use a SCAR barrel.
I hope that you are either being flippant or are referring to the dimensions of some specific part, like a nerf dart or stock vulcan chain. The dimensions are dictated by the design that no one has come up with. Everyone and their little sister can CAD these days, that part is trivial. Spending the time to design, prototype, and revise is what they were asking of you, not simply drawing up someone else's work.
I'm not talking about using it for a dart. From the evidence slug has presented its obvious that this would not work on a dart. I'm talking about the rival rounds and making them more stable at a higher velocity. I only want to use a mill because I want to. I like to work with my hands, that's it.
Woah you have an engineering degree that obviously means you are a god of design and fabrication and make literally anything
I neither have a degree nor am I the god of fabrication. What I do have is a fairly well equipped machine shop and some advanced research equipment. I also have a little bit of fab experience with stuff like automotive intake manifolds, exhaust, and chassis bracing.