A Novel Pneumatic Nerf Blaster Mechanism - Recoil Operated Action

A semi-automatic mag-in-grip Nerf pistol has long been the holy grail in Nerf design. Fortunately, the hobby has come to a point where mag-in-grip pistols are now possible. While many are electronic and rely on tiny flywheels, very few are air powered due to many engineering challenges. This is a prototype design I'm working on that aims to solve some of those challenges in an unusual way.

Difficulties with Pneumatic Nerf Pistols

So why is it so difficult to design a semi-automatic Nerf pistol? There's a couple of obstacles which make it different and more challenging compared to a larger form factor blaster like a rifle.

Dart Size

Dart size is a huge constraint to Nerf design. Before the popularization of half darts, it was impossible to fit a magazine in the grip due to the darts being nearly 3 inches long. Half darts make it possible at last for magazines to be able to be held in the grip. Even still, the darts are larger than one of the largest pistol calibers, the .50AE, and it's always going to be chunky and uncomfortable to hold, particularly for people with smaller hands. Commercial magazines like the Worker Talon are robust, but thick. Custom magazines can be sized better and incorporate an angle, but then you're limited to that magazine only. 

Comparison of full and half darts and magazines

Energy Storage

For any blaster to be automatic, there needs to be some form of energy storage that lasts for multiple shots. In flywheel blasters, that energy comes from the batteries. In air tank blasters, the air tank supplies the energy. However, springers only store enough energy for one shot before it needs to be primed again. This makes them poor candidates to be made automatic.

Air Delivery

Pneumatic blasters require air to propel the dart out of the barrel, which becomes a challenge in mag-in-grip designs because the darts are already in the back of the blaster. This limits the amount of space available for a plunger tube. This is why standard Nerf blasters have the magazines or cylinders far forward. There's a few ways to mitigate this by angling the plunger tube in different directions, but all of them don't flow as well and introduce dead space, which reduces performance.

The iconic Nerf Strongarm revolver. Note the position of the cylinder and lack of barrel

Technology

This is more general, but advancing technology has made it considerably easier to design and build blasters. The rise of 3D printers have pushed the boundaries of homemade blasters past the PVC snapbows and rainbow pistols of the past. The emergence of HPA as a carryover from paintball, especially in the Australian Nerf scene, have greatly advanced the development of pneumatic blasters. And as a whole, everyone is learning new things over time, with even stock blasters tripling in performance. 

Mechanism Theory

This mechanism attempts to resolve the complication of rechambering a new dart after firing a dart out of the barrel. I went with a pneumatic design, as there is greater performance potential, and is more interesting than a flywheel design. Current self loading pneumatic blasters either use the plunger tube as a piston, and retracts and pushes a new dart into the barrel, or uses a separate piston to move the breech. These do not work for a pistol sized platform, as there's not enough space behind the magazine for the plunger. There are also a few innovative designs that use a pivoting lift gate to lift the dart into the barrel, or even a sliding barrel design. However, those have their own shortcomings as well, including wobbling barrels and poor trigger response. This design aims to resolve these issues.

The basis for the mechanism is a standard plunger driven blaster, similar to what you would find in a springer pistol design. A plunger is driven through the plunger tube, which compresses air behind the dart. In this configuration, the plunger tube is inverted, and the air travels through a U bend to get behind the barrel. Instead of a spring, the plunger is driven by compressed air, using a QEV valve and dump tank.

Mockup of the mechanism

The unique part is what happens after the air gets pushed out of the plunger. The plunger is quite a bit larger than normal, and is considerably heavier. The plunger tube keeps going past the air exit for the barrel, and will continue traveling due to its inertia. The plunger impacts the slide, which will be pushed backwards, opening the breech for a new dart. The slide and plunger is spring loaded, so it will return back to the original position, loading a new dart and resetting the plunger. Since the plunger travels past the barrel outlet, any excess air behind the plunger is vented safely out of the barrel. 

The plunger pushes the slide back, chambering a new dart

Benefits

There's a few benefits to this system. For one, it is one of few pneumatic designs that can reload itself. It allows for a long barrel (the one above is 8" for instance), and you can get a lot of power from it, unlike a flywheel blaster. Since the barrel is fixed, accuracy is not affected. It uses standard off the shelf Talon magazines, and allows for magazine changes without pulling the slide back. The system is also scalable to other blaster types without much modification, so it can be put in an SMG or rifle shell. Plus, actual recoil is pretty fun and adds to the experience. Unlike the simulated recoil in most other blasters, this is actual recoil of the plunger hitting the slide. 

Drawbacks

This is far from a perfect solution however. Unlike traditional pneumatic blasters, the compressed air goes through intermediate steps before it gets to the dart. It loses energy and therefore efficiency propelling the heavy plunger back against spring pressure, which softens the initial pressure spike. Plus, the total air volume is limited by the plunger tube size, like in a springer, rather than the technically limitless air volume in a dump tank. The system will also likely need quite a bit of tuning to recoil reliably. Things like plunger weight, return spring strength, tank PSI, and O-ring friction all play a role in how well it works. The recoil itself might affect accuracy, depending on how quickly the dart leaves the barrel. There will likely be a slight pull forward as the trigger is pressed, followed by the major snap backwards when the plunger contacts, both of which could pull the shot since darts travel much more slower than bullets or BBs. And lastly, it's fairly bulky and complex compared to some other designs. Sizewise, it is comparable to a Nerf Retaliator core or a Stryfe, so it's not going to be small. 

Next Steps

This system is still very much in the theory and planning phase, and it has not been tested at all yet. I am still in the process of finding all the compatible fittings and springs to make it work. I hope to procure the parts within the next month and start printing out the first proof of concept. If it works, that's great, and I'll keep on refining it to a performance level I am happy with. If it doesn't, I'll repurpose the pneumatic parts for a more traditional build. Either way, I'm looking forward to adding a new homemade blaster to my arsenal!