I don't know anyone who would knowingly attempt to pull the trigger with an obstruction of any kind in the barrel. There is really no way to see the bullet though - either the chamber stays closed or the next round jams into the stuck bullet and blocks the view of it.
And, this is middling critical.
In a nigh stress situation in the full flood of an adrenaline dump, there is scant little attention for anything outside of that narrow range of focus. A person could go right past pink elephants or tigers in tutus and not notice.
Foveal vision is spooky. It's like looking down a glass tube--the vision is very clear at the mouth of the tube, but very blurry everywhere else. It's visible, but the adrenaline is basically dumping all input from the periphery. You go from normal vision to super sharp in the center, to around 20/100 everywhere else. (The term comes from the fovea, the area where light directly impacts the retina, it spans about 30-35º of a person's "normal" vision--scientists are still undecided on the actual biomechanics of it, but it's a well documented thing.)
So, you don't really have a lot of time for conscious thought, it's more about training and reflexes.
Your training means you expect the gun to come up and go Bang! It doesn't, so it's down to the reflexes and training as to what comes next. If trained (or experienced to reflex) the slide rack will be nearly unconscious. If/when the there's no second Bang! then things change. Either focus shifts from Threat to Gun (poor outcomes); or focus remains on Threat, and Next tool is gone for (better outcomes).
Which could be just using the gun as a bludgeon. Back in the 60s two handed shooting was not "the thing" so very much. So the left (or offside) hand is likely empty. Bun not going off twice being Bad, the gun hand might come forward as the support hand goes for a backup weapon like a knife. This will not include much overt thinking beyond "Knife!"