polycarb

My current version has a sliding trigger, not hinging. It also utilizes a 1" thinwall priming insert, a different rainbow setup, and a tapered plunger rod that sits outside of the catch in the unprimed/resting position. The sliding trigger is smoother and allows for very consistent slam-firing.

A big reason why I abandoned your type of design was to optimize part fabrication and cost efficiency. Every plate on my current version can be built out of sheets measuring 12"x12" or less, eliminating the cost of 12"x24" sheets (and shipping costs less too.) Plus, all of my templates require no overlapping when applying them to the materials. If you've had the misfortune of 2 plates not lining up due to maligned adhesive label paper, you'll know that overlapping templates is a pain in the ass.

I hadn't seen Drev's design; I guess there are only so many things to do with a backward facing plunger and a foregrip.

Earlier on in planning, it had occurred to me that using a sliding trigger lets the whole thing be shorter, after which I realized I was happy enough with this, even though it isn't ideal. As a side note, this is essentially as short as you can get with a pivoting trigger.

Using the thinwall 1" pipe would have been a great idea, if for no other reason than making the catch easier to make, what with more space for it to fit into.
And it did seem to me at one point or another that using 12×12 sheets (and good on you for doing so) goes along much better with a sliding trigger - it keeps functional parts more towards the back and thus needs shorter side plates.

As to slamfire - kinda... When the 1" slide is in the primed position, the trigger pops up into the 1.25" pipe too much. That could've been prevented by extending the 1" pipe towards the front a little more.

Sorry if I missed it, but what are the dimensions on the O-rings?
Otherwise, the design is brilliant, and I'll look forward to making one.
EDIT: It appears that the craft foam is sealing the piston to the outside. Will this seal last for long enough?

The titan has the highest output. I think those are banned at most nerf wars. Correct me if im wrong

They're generally banned if they're singled, assuming the host isn't stupid.
Draconis is definitely right, a Jobar or Pango blaster will have much more air than a BBBB of a titan.
But 4 darts really isn't enough. With the power in a pulse strike or a cobra, you'd probably want to use 8 darts, maybe more.

Particle board is a manufactured wood product. It is actually quite environmentally friendly, as it is built from compressed shredded wood scraps and recycled wood, held together with a type of resin. It is cheaper and more dense than hardwood, but is not very strong or resistant to moisture. It also does not take paint (let alone stain) well.
(For anybody who cares, from http://woodworking.a...icleBoard.htm.)
Also, I doubt it could hold a thread.

So, no, it doesn't seem like a good alternative.

I'd be really happy to see more work and refinement on this in a way that could be repeated with consistent results but for now the best way to get a reliable and quick reload for a shotgun-like effect is to use a turret with the barrels packed with darts or hook hoppers up to multiple airtanks with a linked trigger.

Alternatively, you could make shotgun shells with 2 in PVC and 1/2 PVC, and on the ends of the PVC, put RSCB'S.
Unfortunately, the PVC would have to be heat bent to give the couplers space. At that point, It would be better to use BRISC's.
If your darts and barrels were very consistent, that should work to fire 4 darts at a time. Not only would it be hard to replicate the same amount of heat bend, but your gun would weigh a ton and it would be absurdly front heavy.