Winchester 1873 Main spring tension | Restoration, Repair and Maintenance | Forum

Iv recently gone through and got  a 1873 chambered in .22 short to shooting condition. It fired the first round no problem, but now appears the hammer isn’t dropping hard enough to ignite the cartridge. The screw for adjusting tension on the main spring is completely missing. Iv been unable to find one anywhere and was wondering if anyone knew the dimensions of this screw to see if I can come up with a replacement before replacing the main spring. Any other tips and pointers appreciated!