Designing a Nerf Magazine Stock

 

I will be going over the design process of a Nerf magazine stock. It's a pretty quirky adapter which allows the user to use a spare Talon magazine as a stock. 

The part can be downloaded on Thingiverse.

Inspiration

I saw a video of the Russian PP-2000, which was one of my favorite weapons to use in the game Ghost Recon Online, and I noticed a feature that I had never seen before. In addition to the familiar folding stock, there was a cutout that apparently was designed to hold a spare magazine to use as a makeshift stock. That was pretty fascinating, and seemed like an interesting way to hold more ammunition on the gun itself, which I am a fan of. Thus, I wanted to do a similar thing with my Nerf blasters. 

PP-2000, with the spare magazine inserted in the stock

Initial Concept

The first step was to determine whether I wanted to make it out of a full size Nerf magazine, or a half length Talon magazine. Ultimately, I chose to use a Talon magazine because the full length ones were too large and unwieldy, especially when sticking out behind the handle. I also measured the length of the Talon magazine and compared it to the length of a traditional stock, and they were almost perfect matches. This made the concept seem much more doable. 

I then considered building a completely new blaster to make use of this idea, but that was a lot of work and I don't feel like it's a novel enough idea to warrant an entirely new blaster. Then I decided to make it retrofit on an existing Nerf blaster using the standardized stock attachment point. There was an issue however - springers require extra room in the back for the plunger rod to go through, and therefore had a buffer tube extension out the back. After some measurement, I decided to just make it compatible with flywheel blasters, as building an adapter on top of the buffer tube made the adapter itself too long, and kind of subtracts from the point to have a compact PDW style blaster when the magazine is removed.

Two different attachment styles, Retaliator on top and Stryfe on bottom

Design

Once the design parameters were formalized, I started work on the CAD modeling. I took measurements of the stock attachment point, and made an adapter that would go over it. I then decided on an angle for the magazine to sit in, and it seemed that 15 degrees would be a reasonable angle. It brings the butt of the magazine close to the center point of a standard Nerf stock, and didn't shorten the length of pull too much. Since Talons are asymmetrical, I did some testing, and found that it was easiest to load with the front of the magazine facing down. 

Then I needed to figure out how to lock the stock onto the blaster. I decided to just base it off of how the regular Nerf stocks attached on. Those use a spring loaded plate, which locks into a notch cut in the attachment point. I decided to do the same design, and borrow a spring from my parts bin. The cover to allow access to the spring mechanism would be attached using a single M3 screw, which I salvaged from one of my old Nerf blasters. 

Similarly, I had to figure out the same thing for the magazine. The actual locking nub on the magazine was too far down, and would have made for a fairly long attachment, which kind of goes against the design principles. Thus, I decided to have it be solely friction fit, with a tiny bit of help from the feed lips. This requires much tighter tolerances, but since it's used as a stock, those compressive forces should keep it in well enough. Worst case I can shim the inside a little more for a tighter fit, but it should do well enough.

Assembly close to completion

Prototyping

Prototyping was the next step. To check fitment and avoid wasting filament, I printed out thin slices of the profiles of the attachment point and magazine well. This turned out to be a good idea, since some things were slightly wrong with my measurements. I had assumed the stock attachment point was square with chamfered corners, and it turns out that it was not an exact square, but actually slightly shorter on top by about .05". This meant the fit was too tight, and I had to refine the measurements a bit so it would slide over it well. The magwell slices were somewhat useful, but because of the angle, the total height was actually slightly longer, and the short length of the slices made it not super useful. It was great for checking widths however.

Test fit slices, note the subtle changes in profile

One other issue that popped up was that the release switch for the stock was quite fragile when printed, and broke when I was removing supports. I had measured exactly from the original Nerf part, but those were injection molded and didn't have the same weakness. I had to add material so the layers could stick better. 

Button before on left, after on right

Once I was mostly happy with the dimensions, I printed out the entire thing. The print took just over 5 hours, and used 39 grams of plastic. The interface surfaces had to undergo a bit of sanding for it to move smoothly, but that was expected because of the rough surface caused by supports. Once complete, I was able to do a full test of its ergonomics and usefulness.

Adapter, with Recon stock for comparison

As expected, comfort was not a strong suit, but it wasn't nearly as bad as I thought it would be. The length of pull felt slightly tighter than a standard stock, but it was definitely usable. The angle made it easy to get behind the sights. The friction fit magazine was tighter than expected, but it held it in great. The spring I chose for the stock release was a little long, so it ended up buckling instead of compressing. This made it act more like a toggle switch than a spring loaded switch, which wasn't a bad thing, but was unexpected. After the print, I decided to add a chamfer to the end of it to streamline the design, but since it wasn't a huge deal, I didn't feel like printing another one.

Conclusion

This was a pretty quick side project, and while I really don't have a huge need for something like this, it was pretty fun to do. It's given me some good measurements on stock attachment points and Talon mag dimensions, which I can copy and use in other builds as well.