You MIGHT need the factory hammer spring if you have the Murray aftermarket pin....don't know about the original Russian firing pin springs...never heard of a problem with those...
What I'm saying is the factory hammer spring is only about a 1/2# difference in pull weight in a well tuned trigger with good mechanical advantage (read: no filed on / butchered sear and /or hammer). Since it's the heaviest, it forces the hammer to follow the sear with the most pressure. Conversely, if the trigger is tuned well with the heavier/more difficult to tune factory spring first, then the best work/results is required and achieved. .....metaphor: If a boxer trains at 10,000 feet elevation, he's REALLY fit at sea level.
If I can't get a good feel and reasonable weight with good/safe engagement with the factory spring then there is a mechanical advantage problem and usually a new sear gives me the metal to add to the system.
Hammer springs are easily swapped: put the hammer in the fired position, invert the trigger group, and lock that downward protruding hammer tightly in a vise, push the trigger group off the hammer, swap springs, repeat. I do this in about 5 seconds...
Being able to use both springs adds versatility to the ammo or configuration of the rifle.
Am I making sense here?