[Swordmaker]

You have a worn hand. The reason it works on double action is because the leverage of the double action imparts a fast spin on the cylinder where the inertia of the spin carries enough rotation to engage the cylinder lock... most times. In single action, the hammer cocking and subsequent cylinder rotation are slower, thus not imparting the inertia to the cylinder before the hammer reaches cock and the lock drops early almost every time.

The gun will shave lead on firing and is not safe to shoot even in double action. You need either a new hand or some welded buildup on the old and then a retiming.

[central_va]

This is the exploded view of the Cobra which is the same as the Agent but with a steel frame. Can you tell which part that I need?

I guess #24, right? Couldn't it also be the spring #29 is worn out?