FWB 124 mainspring length ?

[ccluck]

I'm bringing my FWB 124 Sport back into service, after years of letting it languish at the back of the vault. It shoots kinda OK, but I want to get it in top form. I've watched few videos, and read the PyramydAir 3-part blog about overhauling one of these, so I got into this afternoon. Built up a very effective DIY spring compressor and now have the spring in hand, but also have a question.
How long should it be ? The blog illustrations suggest that the spring is roughly twice as long as the endcap-guide assembly, so maybe 12i-sh inches ? Mine measures 8.75 inches. The coils appear to be uniformly spaced. the ends look to be original, not cut off or anything like that.
The blog also says there should be a lot of preload, about 4.5 inches, but this one was completely slack when the compressor was backed off only 1.75 inches.

So, can one of y'all tell me what I've got here, and what do I need to go to original specs ?

 

[ccluck]

OK, so with some additional research I've concluded that I have some version of a tune kit, similar to, if not actually, a Maccari kit. There is a delrin spacer up in the piston to provide some extra load to the short spring. Since everything looks clean and tidy, I'll just replace the piston and breech seals, lube it all up and carry on. No telling when the mod was done, but before 1995, I expect. Could have been later, but that would imply a pretty significant lapse in my memory - hate to think that's true.
Anyway, all is well, but comments are still welcome.

 

[Wadcutter]

Here's a Maccari Pro Mac kit (top), compared to factory spring (bottom).

 

[ccluck]

Yessir, that appears to be exactly what I have, although I didn’t measure the wire diameter.
Thanks for the comparison photo.
In your experience, does this constitute a perceptible upgrade ?