Bobcat - A very-low-hardware single-shot nerf springer

Not every blaster needs to fire darts at 250FPS 50 times a second.

This little guy was created to solve a very simple problem: I want to have a fun little pistol for plinking at zombies with in Humans vs. Zombies.

It achieved that goal better than I could've hoped.

Flicking the action open and closed is tremendous fun as a fidget toy. The blaster is accurate (and I included a PCAR frontend to try out if the normal muzzle piece isn't accurate enough for you). It's reliable as can be - no mags to jam up, very few seals to mess up.

In my configuration (small chunk of 788 spring, enough to rattle around inside), it's just under 100fps. with K25, I'm sure you could do probably upwards of 130-140.

Another key benefit: it's cheap . I mean really cheap. Printed plunger tube, printed barrel. A small handful of screws that you probably already have laying around. Some elastic for the trigger/sear. A tiny piece of spring you could steal from a pen (or leftovers from a Freerunner or Blitz build you've already done) for the top latch. Two o-rings. A very short piece of 788 or K25. The price puts Bobcat in the "why not" category - the fun-to-dollars ratio is very high.

So try it out! If you don't like it, pass it off to someone else - it's not like it was expensive. But you're gonna like it.

Print and build guide: https://docs.google.com/document/d/1wnlONFJnkZgkYew87XMjDCWJLoYUAg_lsjUsqcsfl00/edit?usp=sharing

Changelog

2026-07-26: Version 1.1 uploaded

- Loosened the ID of the plunger tube to fit the 27mm OD o-ring a little better. Reduces friction substantially

- The Plunger Tube and Plunger parts have been modified for this

- Added an elastic-band-powered variant

- This version has its own Plunger Tube, Plunger Rod, "Spring Rest", and extended Barrel

- Since the spring doesn't need to live inside, I was able to make the draw 20mm longer

- On some slingshot tubing I had laying around, I was able to get to about 130fps this way (doubled up and pre-tensioned)

- Aside from the four unique parts, this uses the same files as the spring-powered version

2026-08-06: Version 1.2 uploaded

- Added a hole in the trigger guard for a hex driver / allen wrench to stick through, should make construction easier

- Uploaded an STL with the face seal o-ring's grooves pulled back 0.1mm in all directions. Try this if you can't get the o-ring to go into the channel (printer tolerances, mostly).