What Tomcat said. I've found that there is a wide range of "what works and what doesn't" as regards mainsprings and strain screws on Smiths, especially on the later ones with frame-mounted firing pins. I've also found a fairly wide variation in the length of strain screws in later production Smiths. Therefore, the conventional gunsmith wisdom that a factory stock strain screw, fully tightened, will prevent light strikes ain't necessarily so, just as it is not necessarily true that a shorter screw or one that is backed out a bit will cause light strikes. For whatever reason, I've lately encountered more ammo with overly hard primers than ever before, in several different brands, seeing revolvers with heavy firing pin strike failing to ignite them. But, the rebound slide spring will not affect strike energy.