I recently bought a nice colt Cobra - the one that looks like a Seventies Detective Special, but whose frame is aluminum. Everything was fine dry-firing - in fact, the timing was close to theoretical ideal.
The problem came when I put snap caps in the cylinder; it would occasionally freeze up in mid-trigger-stroke and be unable to complete the firing sequence. I finally tracked it back to the cylinder release latch protruding past the recoil shield - the top edge of the latch seemed to catch in the cartridge head near the "primer" and bind the cylinder. I could, in fact, clear the binding by moving the top of the latch backwards.
Compared to my Detective Special there were three differences. First, the DS latch appeared straight and level (rather than the Cobra's cocked out of alignment) and second, the DS sat flush with the recoil shield (rather than the Cobra's being too far forward, reducing cylinder clearance). Third and finally, the DS latch could be canted slightly forward at the top, but it would return to level when let go of, while the Cobra's would remain canted.
I'm returning the Cobra within my three-day return period, but it does seem to be a minor adjustment or possibly a spring issue. Any ideas about what causes this?