Here is the problem. In order to fire a primer, the firing pin needs a certain amount of momentum, which is velocity x mass. The hammer on a J frame revolver already has low mass (compared to say, the hammer on an SAA Colt), so it needs velocity to fire reliably. That comes from the spring. If you weaken the spring too much, the gun may not fire or may fire under ideal conditions but fail if cold or dirty. I don't say not to reduce the spring tension, but agree that testing is absolutely necessary and building muscle strength is also a good idea.