Lots of possibilities here.....I would start with a complete and thorough cleaning, including disassembly/cleaning of the cylinder assembly. If the gun is not clean, examination and further measuring and evaluation of specs will be pointless.
Embedded shooting debris in and on these parts (particularly the cyl assem) can cause intermittent malfunctions and reliability issues. Give particular attention to the extractor, under the extractor, and the area under the cartridge head. Use a magnifier.
After cleaning and a wipe down, measure the headspace, or "rear gauge" to make sure it is correct. Non-magnum rear gauge should fall between .060" - .068". Smaller is better. Feeler gauge should be placed between the breechface and the rear of the cylinder in the area of the hammer nose bushing. Remember also that endshake can occur on the yoke also, so be sure to check the yoke to make sure it's properly fit to the yoke screw, and it's not moving forward when in the closed position.
Also, check the condition of the hammer nose, and spring, if the hammer nose is fitted with a spring. The nose should move freely. Check the condition of the hammer nose bushing. It may be damaged.
Another possibility is a protruding pin or pins in the hammer or trigger. The drag can sometimes cause reliability problems. If this problem exists, there will be drag marks on the sideplate and/or the frame under the parts. Offending pins can be dressed down or driven back down flush with the part.
Trigger "staging" can also cause problems if you are doing this while firing in DA.
Carter