I have a s&w 38 special from the 1940s that was passed down to me. I had a gunsmith take a look before using since it had not been shot in several years. When I took it to the range, I noticed that when I pulled the hammer back, it would not stay locked back for two chambers. The other four would cause the hammer to stay back until the trigger was pulled with no issues. The cylindar rotates without a problem as well. Any idea what the problem may be before I find another gunsmith to take a look?