Most of the time a squib will not function the slide and cause a jam. The tendency is to clear the jam and keep shooting and that is where you can get hurt or dead. Last week I had a round the did not eject but partially functioned the slide. I had to drop the mag, lock the slide open and check the barrel. You might notice the difference in the recoil. If the round does not eject there is a good chance it did not clear the barrel. By not eject I mean it is still in the chamber. Squibs are extremely dangerous in revolvers where the tendency is to pull the trigger again. There is no jam or malfunction to warn you. Only the recoil and report.
danf_fl; When the police were still using revolvers a range officer/instructor I knew used to make the officers fire their carry load before they could shoot practice rounds. Unbelievable how many squibs, hang fires and failures to fire there were. One of the reasons police went to shooting duty rounds to qualify.