It is my understanding that the changes in the Lg Siler were in both the tumbler and the sear. The tumblr was re-designed to increase the length of travel, giving the flint better clearance at half cock, and to increase the energy delivered to the frizzen. The lock now has better balance so that there is more of an acceleration to the cock on it's way to the frizzen, and less pressure by the foot of the mainspring against the tumbler 's arm at full cock. This reduces the pressure needed for the sear to hold in full cock notch, and thus a lighter trigger pull can be achieved. In addition, the sear arm returns to relatively the same place in half and full cock, which makes it's relationship to the trigger easier to get right.
Maybe it's all just theory. But the locks are much improved to my thinking, than Bud's first design.