UASR

Universal Airsoft Spring Rating System - UASR

So as I'm sure many of you are well aware manufacturers spring ratings can be anywhere from slightly inconsistent to totally fictional. This of course makes selecting a spring difficult at times and doing accurate FPS upgrades challenging without shimming, clipping or short stroking. And more advanced data gathering to better understand the effect spring length, rate and construction has on efficiency is nearly impossible using manufacturer ratings. So to remedy this I've made a Universal Airsoft Spring Rating System, UASR (not very pronounceable I'll admit but it doesn't seem to share it's name with anything too well known, recommendations welcome for something more clever).

The basics:

This system uses a simple 1 mass device to measure the spring rate of a spring and combined with the length and some average airsoft measurements it is used to generate a easily comparable UASR rating value that will hopefully provide very accurate spring comparison across ratings and brands. To make this as accurate as possible this rating is actually equal to the energy stored and released in the spring during firing. The rating system also includes a few other information values that can be used for more accurate comparison and math. These being the measured spring rate, the testing mass used, and the type of spring. Type being linear, dual rate, and progressive (L, DR, and P respectively). For the average user the only thing they need to take into account is a dual rate or progressive spring will be slightly stronger than a linear spring because of the simple testing system.

Example:

So for a ZCI M120 the information looks like this:

UASR: 3.52DR

Rate: 706 (6kg test)

Length:173mm

For most uses only the UASR rating is needed and springs with the same types (the letters at the end) can be compared directly. If the types are different it would generally be something like P>DR>L in that an DR rated spring will be slightly more potent than a L rated spring of the same value. How much more is something for future revisions of UASR to sort out from better testing and feedback.

OK this is nice and all but can I use this now?

Yes! All the springs I have in stock now at Clandestine Airsoft have been tested and their UASR ratings, rates, types, and lengths added to the descriptions. From this testing I've gained some pretty helpful insight into some of these springs. Like for instance the ZCI M180 is the most powerful spring tested so far and in facts tests quite a bit higher than the SHS M190. 10.75L for the ZCI M180 vs 9.29DR for the SHS M190. There is quite a big difference from brand to brand of the same ratings and the linearity even in brands isn't always very even.

Full testing results here

Some more technical stuff:

So the first issue I want to address is the dual rate issue, most aftermarket springs are dual rate and the current revision of the UASR rating doesn't effectively measure the different rates and the transition point, mainly because this is quite difficult without more advanced measuring equipment which I wanted to avoid because I want to keep it so anyone could test springs with very basic equipment. I a, looking into doing the calculations of the rates based on the coil number and spacing measurements but this will be for a future revision.

Another thing I would eventually like to achieve with this project is a better understanding of the how the spring length, rate and construction effects the efficiency of the air system. My theory is shorter springs with higher rates are actually more efficient and because this rating system uses spring energy, ideally with some testing we will see some deviation in performance from springs with similar UASR ratings but different lengths. We could also possibly test how much dual rate or progressive springs effect things and if it is even a positive effect.

How to calculate UASR ratings:

The two values needed are the spring length and the spring constant. The spring constant can pretty easily be tested by simply applying a known weight and measuring the displacement. The mass and distance measurement of course needs to be as accurate as possible. I used a 6kg mass for my testing and digital caliper for measuring displacement. The only other important thing to note here is try to make the device as low friction as possible. If people are interested I'll post more information about my very simple spring constant tester, but I will say 1/2in PVC makes the perfect compression tube.

For the math part I used two rough measurements of 60mm and 120mm for the fully compressed and fully uncompressed lengths in a average gearbox. These are roughly your standard gearbox with AoE corrected and one bearing on the spring. With these you just calculate the total energy with:

(0.5*k*(L-0.060)^2)-(0.5*k*(L-0.120)^2)=UASR

k=spring constant

L=spring length

all SI units

This math can also be used to compare systems with different stroke lengths just by changing the 0.060 and 0.120 parameters.