I have a well used 1967 Cobra that I carry occasionally when I exercise walk. A few days ago, I cleared it and began some dry firing to verify function. At random intervals, the hammer, trigger and cylinder would freeze up, rendering the Cobra useless. After I let off the trigger, it would again function after a few seconds. It would freeze regardless of the trigger tempo. Fast or slow fire made no difference, nor did the interval between squeezes. It might freeze after two trigger pulls, or six or twelve. The lock up seems fine, with very little to/fro or lateral movement with the trigger held back. I'm pretty sure I cannot fix this on my own, but am wondering what might be causing this. No similar issues in the past. I haven't dropped or knocked the revolver at all. On the positive side, my S&W J frames will get some carry time. Thanks.