Chinese models and probably a number of others with custom made
guides, shrink wrapping, cutting a coil or more, spacing, etc.
I use to tinker a bit with the XS B3-1s using this spring, the
Paladin spring and the RWS 94 spring from JM. Sold and gave away
to family and friends all of them. Should have kept one of my
cut down to 8" bbl .22s - fun little thumper!