Find out roughly what fps a spring will give before you fit it. Pick your gun type and spring rating to see the typical fps range on a 0.20g BB, the energy in joules and how it compares with UK site limits. Or enter your site’s limit to see which spring to start with.
What the M rating means
Airsoft springs are usually sold with an M rating, such as M100 or M120. The number is a rough guide to the fps the spring is designed to give in a standard AEG with a 0.20g BB: an M100 aims for around 300 to 330 fps, an M120 for around 370 to 410.
It isn’t a precise standard. The same spring can chrono 20 to 40 fps differently depending on:
- Cylinder volume and inner barrel length: a bore-up cylinder or longer barrel usually adds power. See our Airsoft Inner Barrel & Hop-up Guide.
- Air seal: a leaky piston head, cylinder head or hop-up bucking wastes air.
- Spring brand and wear: springs from different makers vary, and they soften with use.
Bolt-action snipers have larger cylinders, so the same rating shoots noticeably harder than in an AEG.
AEG spring fps chart
| Spring | Typical fps (0.20g) | Joules | Typical class at the top end |
|---|---|---|---|
| M90 | 280 to 300 | 0.73 to 0.84 J | Indoor / CQB (some sites) |
| M100 | 300 to 330 | 0.84 to 1.01 J | Rifle, full-auto (AEG / GBBR) |
| M110 | 330 to 370 | 1.01 to 1.27 J | DMR, locked to semi-auto |
| M120 | 370 to 410 | 1.27 to 1.56 J | DMR, locked to semi-auto |
| M130 | 400 to 440 | 1.49 to 1.80 J | DMR, locked to semi-auto |
| M140 | 420 to 460 | 1.64 to 1.97 J | Bolt-action sniper |
| M150 | 440 to 480 | 1.80 to 2.14 J | Bolt-action sniper |
Bolt-action sniper spring fps chart
| Spring | Typical fps (0.20g) | Joules | Typical class at the top end |
|---|---|---|---|
| M100 | 330 to 360 | 1.01 to 1.20 J | DMR, locked to semi-auto |
| M110 | 360 to 390 | 1.20 to 1.41 J | DMR, locked to semi-auto |
| M120 | 390 to 420 | 1.41 to 1.64 J | DMR, locked to semi-auto |
| M130 | 420 to 450 | 1.64 to 1.88 J | DMR, locked to semi-auto |
| M140 | 440 to 465 | 1.80 to 2.01 J | Bolt-action sniper |
| M150 | 450 to 480 | 1.88 to 2.14 J | Bolt-action sniper |
| M160 | 465 to 500 | 2.01 to 2.32 J | Bolt-action sniper |
| M170 | 480 to 520 | 2.14 to 2.51 J | Over typical UK limits |
| M180 | 500 to 535 | 2.32 to 2.66 J | Over typical UK limits |
| M190 | 520 to 550 | 2.51 to 2.81 J | Over typical UK limits |
Before you fit a stronger spring
Stay within your site’s limits. Every UK site chronos guns before play, and many set lower limits indoors. A gun that’s over the limit can’t be used. Check your result against typical limits with the fps to joules calculator.
- Upgrade the gearbox to match. Heavier springs need reinforced gears and piston, a stronger motor and good bushings or bearings.
- Use a battery that can keep up. A stiffer spring draws more current and lowers your rate of fire. Check yours with the Airsoft Battery Calculator and Airsoft ROF Calculator.
- Re-tune your hop-up and consider a heavier BB. Our hop-up guide explains how, and the Airsoft Range & BB Weight Calculator suggests a weight.
- Chrono after every change, with the BB weight your site uses.
Frequently asked questions
What fps does an M100 spring give?
In a standard AEG, an M100 spring typically gives around 300 to 330 fps on a 0.20g BB. In a bolt-action sniper the same rating shoots harder, roughly 330 to 360 fps, because the cylinder and barrel are bigger. Always chrono to be sure.
What spring do I need for 350 fps?
In a standard AEG, most players start with an M100 or M110. An M100 usually sits just under 350 fps on 0.20g, while an M110 can go a little over it in an efficient gearbox. Start lower, chrono, then step up if you have room. Use the calculator above for your gun type.
What does the M number on an airsoft spring mean?
The M rating is a rough guide to a spring’s strength, based on the fps it’s expected to give in a standard AEG (an M100 is designed for around 300 to 330 fps on 0.20g, an M120 for around 370 to 410). It isn’t a precise standard, so springs from different brands with the same rating can chrono quite differently. Some brands, such as Systema, use their own SP ratings.
Will a stronger spring damage my AEG?
It can. Heavier springs put more load on the gears, piston, motor and battery, and can strip gears or slow your trigger response if the rest of the gearbox isn’t up to it. Pair a stronger spring with reinforced gears, a high-torque motor and a good battery. Our Airsoft ROF Calculator shows how load affects rate of fire.
Do I need to chrono after changing a spring?
Always. Spring ratings are only a guide, and your site will chrono you before you play. Chrono with the BB weight your site uses, take several shots and look at the highest reading. If you’re over the limit, you won’t be allowed to play with that gun.
Power your upgrade
Batteries, chargers, BBs and gas for every kind of airsoft gun.
More airsoft tools
FPS to Joules Calculator
Convert airsoft fps to joules (and back) for any BB weight, then check it against typical UK site limits.
Open the calculator →BB Weight FPS Calculator
Chrono’d on 0.20g? See what your gun shoots with 0.25g, 0.28g, 0.30g and heavier BBs.
Open the calculator →Airsoft Range & BB Weight Calculator
Find the best BB weight for your gun’s power and how far it should reach with a good hop-up.
Open the calculator →Spring figures are typical estimates. Your gun’s chrono reading is the only one that counts.