I have some Star pistols in 9mm.
The Star Super B I put on the mill and bored out the recoil spring cowling so I could fit a recoil spring with larger coil diameter. That was for shooting 9x23mm. I also reamed out the chamber.
A good source of springs is Wolff gunsmith kit #14.
http://www.gunsprings.com/General%2...ol%20Recoil%20Springs/cID4/mID132/dID399You might want a little more recoil spring force.
I measured the coil diameter and the wire diameter of the springs I received.
Wolff #14 right .252x.031x cut 3.3/11.9#
Wolff #14 right .434x.045x cut 5/15.4#
Wolff #14 right .390x.042"
Wolff #14 right .358x.046"
Wolff #14 right .315x.040" 0/9#
Wolff #14 right .277x.034" 3/13.5#
Wolff #14 right .266x.031" 4.2/11#
Wolff #14 right .266x.031" 6.5/14.7#
Wolff #14 right .239x.029" 2/10#
Wolff #14 right .224x.027"
Wolff recoil spring for Star semi