Working on these guns is not rocket science. They are fairly simple mechanisms, and easy to fix if you have a parts source for any broken parts. Operative word is "parts source" You say the cylinder spins freely. In which direction? It's supposed to spin freely counter clockwise, but not clockwise. If it spins clockwise, you have a broken, or well worn, cylinder stop, or broken cylinder stop spring. Open the latch, tilt the barrel down like your bottom photo, and look at the cylinder stop, which is right above the trigger in the bottom of the frame. If it not broken, you will see a small metal tit sticking up just a millemeter , or so, above the level of the frame.When the barrel is closed, that tit will align with the cylinder stop notches and stop the cylinder in alignment with the barrel for each chamber, when the gun is fired. If it is not sticking up, then it is broken, or the spring that pushes it up is broken, or there's a whole bunch of old crud clogging up the working of the parts. If the cylinder rotates when the trigger is pulled, that's good, but what does it do when you pull the hammer back to full cock? The cylinder should be locked on place then and can't be turned. If you can spin it with the hammer cocked, you have the broken parts senario described above. The rule in all gun problems is to first identify the problem, then you can seek the solution. Unfortunately S&W constantly changed the size, shape and function of many parts in the 5 varaitions of the .38DA over the life span of it's production. Parts from junker guns, or ordered from Numbrich, etc, quite often are the wrong part from the gun you are trying to fix, althought they are the same model. Replacing small springs is not a problen as they are easy to make or can be filed to fit from a box of generic springs ordered from Brownell's or other dealer in gunsmith parts. A broken cylinder stop can be a real headache in trying to find a replacement. Nobody makes new ones and there are several different styles in the .38DA revolvers that won't interchange. Murphey's Law works quite well when it comes to GunSmithing 101, but perserverance is your best tool. Good luck!