Springing into Action Redux: Springs and Spring Ratings Explained

From the well-known and versatile K26 to our own custom OOD springs, it can take a lot of work to know how your spring is going to perform and how difficult your blaster will be to prime as a result. This is primarily because of how the foam-flinging hobby started, where many parts had to be sourced from hardware stores, paper catalogs, and word of mouth, leading to misinformation and confusion. With this blog post, we’ll attempt to clear some things up for newer hobbyists, talk about why we're changing the naming of springs on the shop, and hopefully make it easier to talk about different springer mods and mod parts while we’re at it.

Common Types of Springs in Nerf

First, many types of springs are out there, and all of them serve different purposes. The most common spring types used in the hobby are compression, extension, constant force, and torsion. An easy way to remember the difference is to imagine holding either end and feeling which movement the spring resists more.

Compression springs are the standard spring you probably think of when you think “spring.” They’ll most likely have squared-off ends from the factory, and they are meant to provide resistance when the ends are pressed together or compressed. These are most often found in the plunger tubes of many a springer, behind the follower of a magazine, or if you were like me as a kid, these were in the ballpoint clicky pens you took apart and reassembled when bored during class.

Extension springs provide resistance when pulling the two looped ends apart – or extending the spring’s length. Extension springs are what keep the fabric of trampolines taut. In community blaster designs, they are used for magazine releases and in the quick-extension system of the Sliding Arm Mount (SAM). In a looser sense, stringer blasters and other mechanisms in community blasters (like the SLAB’s catch and trigger systems) use the extension-spring-like properties of elastic bands to work without the space that conventional extension springs might require.

Unlike the previous examples, constant force springs look quite different from the platonic image of “spring.” Instead of coils of wire looped on top of each other into a column, constant force springs are usually flat pieces of metal coiled into a disk shape. As the name implies, these springs provide the same resistance force no matter how tightly they are coiled. This is great for precision mechanisms, like those in a manual watch, but in the hobby, they’re used in drum mags and cylinders – like the Worker Hurricane’s unique revolver cylinder mag.

Torsion springs are the rarest to want to mess with or replace in our hobby, but they're common enough to warrant mentioning. They store energy by rotational compression, where it resists pushing the two straight ends of the spring closer together. You can find torsion springs used in the catch and trigger mechanisms of most stock blasters, and they are in that annoying half-prime lock you fight with when priming the Nerf Rival Kronos. Alternatively, in the old Nerf Vortex blaster line, they're the primary spring used to directly propel the disks out the barrel instead of using the compression spring and plunger tube found in most springers of other ammo types.

Spring Ratings

Naturally, it’s important to know how springs are rated so you can adequately compare one to another (all else being equal, of course). Manufacturers of springs use a standard rating system across all of them called a spring constant. Depending on their customer base, they’ll use either US customary or metric units to describe how much weight of force is required to move a spring a certain distance away from its resting state.

For instance, the suspension system in many North American cars manufactured before 1996 rated their compression springs in pounds per inch (lbs/in). According to my research, many springs manufactured and sold in sizes modders might use in their blasters, the global industry standard rating outside the hobby is kilograms per millimeter (kg/mm). Oftentimes the “/mm” gets dropped and shortened to "kg" for simplicity’s sake, but they still refer to the same unit.

However, many blaster tag enthusiasts over the years have muddied the waters with their own "kg" ratings. From kilograms per centimeter (kg/cm), to kilograms per inch (kg/in), to kilograms at full compression, any spring used in our hobby with a "kg" rating in their name may not refer to the same measurement let alone its spring constant. An earlier version of this blog post was retracted because of the conflicting use of the "kg" unit. But that's not all.

Ideally, if all springs were rated by their spring constant, an 8kg Lynx spring would require 8 kilograms of force to compress a single millimeter. Assuming that's true, that rating would only theoretically correlate to the practical strength required to prime the blaster. Most types of springs require more force the further the ends have moved away from their resting state. So, while the example Lynx spring above is rated at 8kg, it takes a different amount of force to compress the spring to the point the plunger rod catches. In fact, the type of prime the blaster has makes more of an impact on its prime weight than its rating.

We only recently purchased a spring force tester to help unify compression spring specifications across the website. However, a more easily measurable constant between springs of the same cylindrical dimensions is the wire diameter or spring gauge. Starting this week, our first step to unifying spring listings is to remove all kg ratings from our product titles and replace them with the spring gauge (in millimeters). Later, we will confirm the spring constant, and note it (and all other measurements) in the specifications to tell a better story of how strong a spring is. 

To their credit, Worker has also moved away from their kg rating and have started using the wire diameter for their newer springs, like for the Worker Harrier and Seagull. XYL has followed suit with their unicorn upgrade springs, making this decision even easier for us.

What does this have to do with K26 or other K-Series springs?

Now, for the “K__” Series of springs (and the 788). The names of K26, K31, and other compression springs originated from SKU numbers in McMaster Carr, a common hardware parts mail-order catalog service that the old NIC folks used to purchase parts for their blasters. Those titles have been grandfathered in because of their popularity, but these catalog numbers have no relevance to any spring ratings, especially since it’s common to cut these springs down to the desired size.

Side Note: Spacers & Tuning Caps

As we were saying earlier how most springs change resistance based on how far they are moved away from their resting state, you can use this material property to your advantage. By changing the length the spring rests in the plunger before it’s primed, you can adjust the capacity of stored energy your blaster has, varying the performance with the same spring. This is called pre-compression. While this also changes the strength required to prime the blaster and can (in some cases) lower the spring's lifespan, it’s often a preferred option for those who want to dial the FPS of their blaster up or down without carrying multiple springs to games. For example, we sell specially-designed FPS tuning caps for the original Adventure Force Nexus Pro, the Game Face Trion comes with similar spacers right out of the box, and we recently started selling spring spacer that work in the Adventure Force Nexus Pro X.

 

Okay, so how does all of this affect my FPS?

Like different crush cages across different flywheelers, asking “what FPS is this spring going to get” on its own doesn’t make much sense. Many factors, including the resting length and pre-compression of the spring, the inner diameter and length of the barrel, plunger volume, and even dart choice, can change the FPS rating of a blaster. This is one of the reasons we kept using kg ratings on the site: If the spring fits in multiple blasters, one of the only measurable differences between each spring was their kg rating.

When listing spring options on products where we can control enough variables, we will try to list the FPS we got with our standard 20-shot average testing procedure for that spring. In other cases where we can’t mitigate variables, we’ll list the spring dimensions and a conditional FPS rating (with details of what setup we used) in the specifications so everyone can make an educated decision.

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We hope our work unifying spring measurements across the site will help make choosing springs much easier. At the very least, we hope that our direction of deemphasizing kg ratings on our shop will encourage the hobby to use more practical units.  if you have any further questions, don’t hesitate to contact us.
- J Perry Heun