Think Airsoft Article 1
The Science behind Airsoft Springs

One Airsoft spring is better than another; it’s a question or more accurately a statement I often see on the forums. Why is one Airsoft spring better than another? Different manufactures, standard springs, linear ones, non-linear ones, variable pitch, and plated colours. With so many different springs how do you decide which is the best for your gun. We provide some spring facts and there relation to Airsoft.

Terminology

Rating – This is the term for the strength of a spring, Spring Rate is the amount of weight needed to compress a spring a certain amount. Springs are rated in LB/in or specifically, how many pounds of weight are required to depress the spring by one inch.
Free length – this is the overall Length of the spring, which is determined by the space between coils. You have to understand this is not the true length of the spring. Example Spring A: has a free length of 10 cm and 10 coils, Spring B: has a length of 15cm but only 8 coils. Spring A: is longer when full compressed. This is important in Airsoft, when a spring is fully compressed in a gearbox, as there is only so much room between the cylinder head and the spring guide. Too much length and the piston won’t clear the gears teeth.

Spring wire diameter – This is the thickness of the wire used, thicker the wire the stronger the spring.

Inside diameter – This is the inside diameter of the wire.

Outer Diameter – This is the outer diameter of the wire. Some times companies will increase the diameter to decrease spring strength. Other times they will specifically make a spring a certain size to fit a gearbox.

Inside and outside diameter can play an important role when you are trying to upgrade a spring in a gun which doesn’t have any obvious spring choices available. A quick measure and you can order a spring from another gun with the correct dimensions, a lot of the sniper owners use this method.

How do I choose the right power spring for my AEG?

When springs are made they don’t have Airsoft strengths, they have ratings as mentioned in lbs. And from that first spring created they thing increase by percentages. 100% stronger, 120%, 150%, 200% etc. Some spring ranges will advertise in a percentage. In these cases you’ll need to know what one produces then you can apply the percentage to all the others.
In most cases some boffin somewhere invented the M rule for springs, Don’t worry I’ve tested it, it works and give or take 10 fps its pretty accurate.

We all know an m90 spring produces slightly less than 320 fps and an m100 should be 330 fps or over.
So let’s test case the M rule for calculating what spring to use.

Calculation – Spring m rating * 3.3 = Estimated FPS
90 * 3.3 = 297
100 * 3.3 = 330
110 * 3.3 = 363
120 * 3.3 = 396

We know from actual experience these calculations are RUFFLY correct, remember every gun is different, all with varying degrees of air seal quality and upgrades.
Tightbore’s a golden rule is +10fps
But it’s a good guide for choosing your spring.

Will my spring lose power over time?

Well a spring is coiled wire, which is then heat treated to remove the settling from it.
You have to understand that if held in a compressed state every spring will lose strength, you cant avoid it.
Always fire one single shot in semi before you put your gun away. If you don’t, don’t blame your spring when it loses power.
The spring is a working part therefore it is consumable. If you get 3 years in and your still on the same spring, rather than complaining about the spring, it might be time for an upgrade, 10 pounds every 2 – 3 years to keep your aeg at full strength? Small price to pay some might say. It’s about time we started having standardisation in Airsoft. You wouldn’t run your car for 3 years without an oil and filter change.

The heat treatment process.

This process bakes the springs, which removes the potential for a spring to lose its strength. The actual cost of a spring to make is very small, but the heat treatment process takes an hour per process. Imagine how much it increases the cost of a spring by adding multiple heat treatment processes to remove any potential settling from the spring.
The McLaren F1 springs in the valves, have 100 heat treatment processes, and will never lose any power. But they retail at nearly 80 pounds per 1inch spring. Imagine if your AEG spring cost 80 quid.
It’s just note financially viable, so expect a “certain” amount of loose over time, which IF its going to happen will happen early on.
After installation, fire your gun in full auto, and leave it half cocked over night… if your going to loose some getting it settled and out the way with before your first skirmish, then when you chrono its should be your final FPS figure for the foresee able future.

Choosing a manufacturer.

You simply have to trust that manufacturers are doing their utmost to make sure you get a quality product. You can pretty much assume the higher the quality of manufacturer the more processes will have been added to springs. Look for words like heat treated on the packaging.

Liner and non linear springs.

Linear
A standard TM spring is a linear spring; this means that the space between coils is even, the rating of the spring will be the same at the beginning as it is at the end. This makes the spring initially harder to pick up by the gears but its power rating is constantly the same throughout.

Non-liner or variable pitch.
These springs have a variable rating which has to be worked out via an average. But it means that different portions can be different ratings. For instance the first part having very little strength means it’s easier for the gears. But these springs by their very nature won’t be AS consistent as a liner spring.

Cutting Springs

It’s worth mentioning people are still using the cutting spring method. It was a tried and tested method many years ago for reducing a spring’s power if it was slightly over. Nowadays Airsoft is truly global, and there are springs on eBay, online, at your local shop and at your local site. They are everywhere.
If your spring is a few FPS over try the limit, try firing in full auto and leaving it compressed over night or even a week if you really want to knock some FPS off it, this will reduce it by up to 10 fps.
If your spring is over 10 fps over please don’t be lazy and buy a new spring.
When I’ve cut 3 coils off and then placed the spring on a load test machine, the machine errored out and produced a broken message on the screen. Yes it works but it truly isn’t needed nowadays. Spend £10 at your local shop and get the next spring down. It’s always best to get the spring below what you’re aiming for then fit upgrades to achieve the desired FPS.

With the science behind the springs we can make our own informed choice rather than rely on forum opinions which are usually misinformed.