Disassemble your gun and use the barrel as a cartridge gauge.

A resized case should drop into the chamber with no resistance and the head of the case should be just below flush with the end of the barrel hood.

A loaded round should drop into the chamber with a "plunk" sound. The head of the case should be just below flush with the end of the barrel hood.

The barrel hood fits very closely to the breech face of the slide. If the round sits above the hood, the slide may not close. If the round sits more than a slight amount below the hood, the round may not fire as the firing pin can not reach.

Michael