I know this for a fact. lol
WHile having an operation performed on my toe, the doctor used a nerve block at the base of the toe. He was showing his young PA apprentice how to do so. He told him, push in until you feel it hit the bone. (I fucking felt it hit). He then said to draw it back just a bit as not to put too much pressure on the fluid you are trying to inject.
Only he failed to draw it back enough. The pressure mounted up in the barrel and the syringe blew the pin off. The 18g pin was still stuck in my damn toe. Deadening shit was all over the place...except in my toe. So then he goes and loads another barrel...attaches it to the pin and pulls out just a hair. this time it worked (thank God).
So yes, you would feel it when you hit...and the shit wouldn't flow at all.