I've never had a squib round. I've had a couple of 'puffers' but they always got the wad out of the barrel.
We weren't that precise with our shotgun rounds. The doctor that stitched up my eye suggested that I never use dynamite to blow stumps and that I not load shotgun shells. I didn't, but I had a partner that had a high end loader and I'd help him with everything but the actual lever pull.
We would occasionally have a powder charge or a shot load fail to drop. Most of these we'd catch right away but I had at least two make it into my gun with no powder. We used a light charge (.75 oz) and it wasn't easy to tell when the shot was in. I was in charge of gathering and loading the boxes so I KNOW exactly who to blame :)
I have never loaded a shotgun shell, all my ammunition production has been rifle and handgun. I guess the process is the same. Just different.
The biggest difference is the crimp. Gotta have the machine/collets for that.
Yeah, it's different in that way. The projectiles are encased. I don't shoot much shotgun really, so just buy my shells off the shelf.