The Model 1877 Colt ("Lightning" -.38 Colt and "Thunderer" - .41 Colt*) was a very poor design, even for that time. It is complex and very unforgiving of any wear, which is why so many are found in an unserviceable condition. When new, they work OK, though the old flat springs are a problem, but with wear the timing of the whole mechanism is thrown off and new parts (now unobtainable) will be required. Note that most of the parts sold by the parts companies are either new-made and require extensive fitting or old parts that are themselves worn out and unserviceable.
Jim
*There was also a .32 version, called the "Rainmaker; supposedly only some 300 were made, and I have never seen one. The names were used by Colt's distributors, not by Colt, though they did use the name "Lightning" for a pump action rifle.
JK