I appears you have a piece that has had an action job by someone who knew enough to tune the main spring and set it for a particular load. This set up obviously failed to meet your needs and therefore would not ignite mag primers.

Here is a suggestion that will cost you no more than a new strain screw. Put the mainspring and rebound spring back in the gun along with a new full length strain screw. Screw the strain screw in until you get ignition with mag primers like you want or if you know how to measure the hammer pull/load with a pull gauge set it for about 42 oz. BTW is this a target hammer ? if so add about 4 more oz of pull. With the new strain screw you can begin filing a bit off until you are close then when the gun shoots okay and the action feels better just Loctite the screw in place ( blue Loctite ) . It not a perfectly set up and cut to length screw but it will work and should stay there if you Loctite it correctly

Good luck