I have a workable explanation for the FTF on this gun the other day now. It's something I remember hearing about as a kid in backwoods Pennsylvania the 1960s, but that I don't remember hearing folks talk about much since. A "short-shuck" will cock the hammer but fail to eject the spent cartridge. And, evidently, it's fairly easy to do if you're not familiar with a particular type of pump mechanism. I'm going to function test the gun again to confirm the theory, but I expect this mystery has been solved. I am so grateful for the depth of knowledge that is represented and unselfishly-shared by the members here.