To make a long story short, I worked for about an hour to get into position on a doe I was going to take, only to experience a FTF (which caused me to get busted by the doe). I have a bolt action slug gun (Marlin 512) and I've never had a problem with it. Not like it gets fired nearly as much as a pistol would though. The gun has an indicator at the rear of the bolt to you let you know the firing pin is ****ed (kinda like a Springfield XD does), and when I pulled the trigger, the "click" was just as loud as it always is when I dry fire.

I examined the shot shell, and there was indeed a firing pin indentation on it, though not as deep as one from a discharged shell, it was evident that the primer was struck.

As far as the depth of the indentation goes, well, I guess that's my question. What should a properly struck primer that didn't fire look like? Would the indentation be just as deep as one that had properly fired? Or would it not be as deep as on a primer that had fired? For some reason, I'm thinking that something occurs when the primer goes "boom" to allow the firing pin to sink in more.

Later on, I chambered the shell that failed previously and it went boom. Go figure...