I just purchased a Colt .357 that appeared to be in great condition. The first day I shot it using .38 Special it was great. Today, after putting about 50 rounds of .38 Special and .357 through it the trigger began to stick in the pulled position after firing. I cleaned it and it still sticks about half the time dry firing and the hammer will not stay cocked in single action about half the time. Anyone have any clues?