I have never see any type of springs on the firing pins either, but do not have really early pivot opener guns to inspect. Earlies gun in 21,00 range - 2 hook. I have only experienced the pin hanging problem that you mention a few times, but usually the extractor pushes the pins back as you close the gun so that the shell rims don't catch. In 16 gauge I normally reload Winchester compression formed cases. I suspect the Cheddites are probably larger and not fully dropping in the chamber? Maybe try resizing in a Mec Supersizer or try a different hull.
