That is very interesting! Did you happen to publish the results of those tests anywhere, or keep the documentation? I ask because this is in stark contrast to other comments I've read and I'm guessing it may have something to do with the total case volume of the empty round in question? Maybe you tested with a 30-'06 but with a 223 it would be a different story? I'm not saying it would, just speculating.
No and yes. We tested every rifle I had access to. Without fail you could not even tell the primer fired by sound. The mechanical sound of the firing pin dropping/hitting was the only sound.
I think the term squib load is mainly referring to cartridges with a very small amount of powder and probably in handguns. Not enough smokeless powder in a rifle cartridge can cause an explosion in and of its self.