First, the kilogram is a unit of mass, not force. This is a common error. One presumes they mean something like 2.2 lbf or 9.8 Newtons.
The original coil type recoil spring was not a linear spring, hence the force is not directly proportional to the compression.
The "rated" or loaded force should be measured with the spring compressed to a length of 50.00 mm or 1.33858 inches.
The preloaded force should be measured with the spring compressed to a length of 34.00 mm or 1.96850 inches.
The free length should be 85 mm +/- 2.5 mm.
The preloaded force is seldom mentioned but is fairly critical to proper operation. This will tend to go wrong if you cut an original spring.
The Wolff springs have a free length longer than the originals and are thus much better for cutting down as the preload will not suffer so much.
For the 7.65 with four inch barrel the preload should be 15.4 to 19.8 lbf and the loaded force should be 33.1 to 36.4 lbf. This may prove to be a bit stiff for current factory ammo. When reducing the spring force, the object is to reduce the loaded force while reducing the preloaded force as little as possible. This is why it is better to start with an over length spring like the Wolff when you start trimming.
I don't have full specs for the 9 mm but preload should be no less than above and loaded force should range from 36 to 40 lbf.
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