I found another source explaining it from experience: https://www.grandin.com/humane/cap.bolt.tips.html

It seems that we may both be partially correct: If a penetrating bolt is used the animal is killed instantly. If a non-penetrating bolt is used, the animal sometimes revives. What we don't know is how prevalent each approach is. Either way, re-reading your initial post that I responded to I realized that this debate doesn't matter. Your point seems to have been that they don't feel pain as they're killed, and I concede that you're correct. I missed that this was the point you were making, and that you were not mainly arguing whether the animals were killed instantly or not.

Edit: Just to add that I concede the point that they don't feel pain only in a general sense. Looking at that last link, it seems that this procedure would have a lot of room for error and I'm sure that as a consequence a lot of cows suffer unintentionally.