TP9SFX Spring Options
These are the springs that I have used and tested. Your mileage may vary based on your ammo load.
1. Wolff Cold Commander - 13LB: item 42213, 14lb: Item 42214 & 15lb item 42215https://www.gunsprings.com/COLT/COMMANDER%20SERIES%20PISTOL/cID1/mID1/dID2