I have not yet loaded a squib, or had a primer I seated fail to fire.
I did have a .357Mag round stick a bullet in the barrel, but it was one of 2 rounds my "Mentor" at the time gave me and said 'here try these' The first one made a funny noise, I cranked back the hammer (Ruger Blackhawk) on the second one and my brain interrupt said 'that didn't go right'. I gently lowered the hammer and unloaded it, and pulled the cylinder to check the barrel, There was a bullet stuck in the barrel. Sadly I did not have any way to push it out so I had to go home. Pulled the bullet on the other round, NO POWDER! That was the first and last time I trusted his reloads.