[ars]

The brain shuts down within seconds, not minutes.

It takes a few minutes for it to die, but it's totally unconscious for that time.

And I prefer to look at actual usage, not perfect usage.

For example: http://dx.doi.org/10.1016/j.meatsci.2008.07.016 for this type of animal 53% of the time the stunning did not work properly.

And according to http://www.viva.org.uk/campaigns/slaughter/std4.htm 5-10% of captive bolt stunning does not work properly. There are plenty of other sources that say the same thing.