Springs! Why so much variation?
 

I'm trying to figure out what to do! I bought a bunch on airsoft springs they are all Modify springs, I have a s90, s100, s110 and s120.

Now I want to change the spring in my KWA G36c to get around 330-350 fps.

My results:

S90: 280fps
s100: 360-370fps

Now why do I get such a big differene between the 2 springs? The s90 spring doesn't have tighter coils anywhere, so there's no right way of putting it in, right?

Which other brand should I try? What brand would give me consistent results?

but the s100 in backwards and voila it drops about 20-30 fps

I tought about that, but I wanted to know if it was normal, or if I had a bad spring...

The FPS for a particular spring is related but not limited to many variables such as Piston O-Ring seal, air nozzle seal to the cylinder head port and hop-up rubber, etc. With this in mind the Modify factory tests results were (after 30,000 bbs fired):
S100+: 369
S110+: 405.9
S120+: 443.75
S130+: 470.74

My Modify S90 does have tight coils near the end, I don't if it's because I got mine in a latter batch or something. But I'm getting 345 fps ratings with it.

Thanks for the info... I'll check everything again...

But the readings seems fine for the S100 in your OP. Must be your S90 that is faulty.

That's what I was thinking.. The difference between the 2 is way too big...

And just for reference for Jackarutu, I was also getting 385-390 with a S110

I'm also getting 390-400 with an s110 in my M4.

Barrel length and other air related items affect velocity too, is why ballpark numbers are given on average.

I am getting 340 fps with my S90 and 380 fps with my S100, so I would as well say there is something wrong with your S90.

The power ratings on springs are a bit wonky....

(I might be wrong with some of this)...The baseline was referencing 1Joule with a 0.20g BB. I always thought of it as the "TM base level" because their rifles all shot that hard out of the box.

This was approx 300fps...or theoretically 90m/s. So 110% springs were 330fps, etc... M100 springs were 330fps, etc...

But those numbers were based on different builds from what's "typical" today.
A LOT of builds now have bearing spring guides and tightbores installed...just some of the things that can "modify" the resultant FPS of an AEG.

There's even rough rules of thumb...such as add 7-10fps for a tightbore (that is going from a "stock" 6.08mm inner to a 6.04mm inner)...or add 10-15fps for a bearing spring guide (that is going from a "stock" flat TM spring guide to one with a bearing stack).

So....take a m90 spring and toss it into a stock "TM" mechbox and you're likely to see 300fps. Stick it into many of the other "stock" mechboxes and you're likely to see 330fps. Bad springs? Bad mechboxes? ...not really, just different parts inside.

The original post about the wild differences is still very valid....the M90 seems low. Modify S90 springs do have a tight pack of coils (IIRC)...that should go at the rear.

370 seems high from the KWA...I'd easily imagine 350-360 though with the parts in their mechboxes. But if compression and everything else is bang on you could hit 370.

I've also had the odd wonky spring that seemed way overpowered for what it was labeled...it could always be that as well....but I'd guess you got a wonky s90 spring.

In my two MP5s, I got 330fps (229mm barrel) with the S90 and 360fps (330mm barrel) with the S100, so looks like we are getting a good list of averages here.

Some companies' numbers seems to be related to % compared to the 1 Joule thing, while others like Systema have the metric speed in the numbers, so a Systema 120 will do about 120m/s which is roughly 400 fps.

That's how I see it actually.