Why can two contact gages give different thickness readings?
The gages may contact and load the specimen differently. Contact shape, force and, for compressible materials, loading duration can affect the reading. Flat contacts may bridge local variations. A soft curved shell should not be treated as a rigid flat calibration artifact.
Specify tip and anvil geometry, support and force with the measured feature. Agreement between contact and optical results in one setup does not validate a contact arrangement for every shell. Investigate a result difference before classifying the capsule as defective.
Can a capsule closing-force setting specify the gage force?
No. Closing force concerns joining the cap and body; contact measuring force concerns loading the specimen while taking a dimensional reading. They act in different tasks and cannot be substituted because both are expressed in newtons. The measurement arrangement must be selected and characterized for its own purpose.
Compare force, loading duration, contact geometry and support together. Lower force may reduce deformation while changing how reliably contact is established; evaluate that balance on the actual shell and fixture.