Moon clips come in several thicknesses, from 0.038" to 0.048". The most common are 0.038" and 0.041"
You should determine which thickness is compatible with the headspace of your revolver.
If you are using military brass (or range brass), the pockets may be loose because someone reamed them incorrectly. I use a Dillon Super Swager. If the pockets are tight, the swagger will resize them without removing metal. If okay or too loose, the swagger will not make them worse, and you can feel the tightness in the lever. A reamer will always remove metal, even if not needed.
Oversized fire holes will cause primers to back out. Again, this might be caused by improper case preparation. I bought a bunch of .45 Colt cases one time, marked for use as blanks. The fire hole was nearly twice the diameter of the correct brass.