Does anyone know the dimensions the “M” (M90, M100, etc.) rated springs from M90 - M150? Thanks
Dimensions for springs with the same rating can vary between spring manufacturers
In the windsoft world
- m100 is supposed to send the projectile at 100m / second
- m110 is supposed to send projectile at 110m / second
How the manufacturer achieves that “rating” will depend on their spring design, material used in manufacture and manufacturing method.
For example a progressively wound spring will have a different thickness than a spring that is wound with “equidistant” coils.
That is the theory. Based on fps delivered, all springs designated M100 do not produce the same performance at the muzzle
Yeah even back in the day when we were grading them by wire diameter they were all over the place for FPS.
It’s pretty much trial and error, you bung in whatever works best in a particular blaster. 
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Yes they varied so much there was no standard until the likes of the AG series came out and then we could get some consistency.
An M series from one manufacturer of a 90 series compared to a supposed 90 series of another the specs were wild. The spring stiffness, it was a shit show, buy an M90 acts like a M120 busting 400fps like wtf. OAL variances, spring stiffness variances. All over the place unless you bought high quality airsoft M series springs and dialed in for that and stuck with it.
Made for many interesting discussions on the old forum. Measuring spring wire diameter from the same place, same M series nope mines 1.2mm, nope mines 1.4mm, nope mines black, nope mines silver oh my lordy 
Why does it matter is the best question?
It doesn’t… unless your have a heap of springs with no idea what they are? But then you just have to give them a go to find out.
It’s a bit wild out there… the m rating is a good idea, depending out how the manufacturer tests it… Which is going to be an Airsoft BB of some weight, through a barrel so long with a certain cylinder port…
The SHS red packet version are my favourite spring as with a gel and correct cylinder and barrel length volumes they do what they say… eg: an m100 will do 100metres per second… with certain exceptions.
The blue packet SHS springs sort of do too… But are sometimes a bit of a wild card.
Anyway for red pack SHS…
M100 is 1.3mm wire diameter
M110 is 1.4mm, and m120 is 1.5mm.
And all that means jack shit. As another brand spring… will achieve the same potential through thicker or thinner wire with a shorter or longer spring with the coil spacings differing… and measure it however they do.
I’ve even seen springs where the overall coil diameter is so tight it jammed on a spring retainer, and so large they jam inside a piston!
No standards, just educated guess for us.
I remember in early gel days buying a 1.2mm spring hoping for just a slight boost over than standard 1.1mm spring in a gen8… and it was longer and thicker… Similar coils but the material was noticeably different… and it was actually a fps loss to use it.
So yeah… the measurements mean stuff all.
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The only reason it matters is for consistency. If someone asks what spring you should use and you recommend one from a certain supplier then they get a completley different animal to what you have then… the rest is history.
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The M rating is the meter per second for the series of spring installed to a particular AEG. The AEG used by different manufacturer is not the same. It only give you a very general idea about the Velocity it pushes.
The same dimension for different branded spring may not be the same due to different material as well.
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