OK - law of averages - factory ammo and squib - VERY unlikely. Almost impossible.
I however have had contact over the years with Mr Murphy - and know that his plan is to screw up anything you do - to the max
Let us assume - for discussion' sake - that your first (defensive) shot thru a semi - is a squib and you do actually realize it. You do not (again thx to Murphy) have a BUG this day.
WTH do you do??? In my book I am screwed, royally!!
On reflection - no better off if in a revo!!!