Yesterday at the range, I had a click instead of bang with one of my AR pistols. Immediate 'tap-rack-bang' drill resulted in a failure to go into battery, which a brisk poke at the forward assist didn't cure. OK, time to strip it down & see why it choked. Seems that it had something stuck in its throat:
Perfecta 55 gr FMJ, which I'd found to be adequate plinking fodder up til now. Apparent QC problem with missed powder charge.
The spooky thing here is that I heard no 'pop' from the primer, just a dry click. I'd always assumed I'd hear the primer pop in a case like this, Nope.
So, I'd have to say that any failure to go into battery after a T/R/B drill needs to be assessed, don't just beat the next round into battery. Excessive drama & unscheduled underwear change might otherwise result...
As far as not hearing the primer if you were wearing hearing protection that's not to surprising, especially if there were other on the line firing beside you. Since the bullet didn't exit the bore and the action remained closed the sound is going to be muffled pretty well in the situation.
I few year's back while hunting with my muzzle loader that uses shotgun primers my powder got wet and would not fire. I fired several primers until it apparently dried it out enough to push the bullet and mostly unburnt powder pellets out the muzzle. I was surprised at how much sound it DIDN'T make.