According to SAAMI, “A cartridge or shell which produces projectile velocity and sound substantially lower than normal. May result in projectile and/or wads remaining in the bore.”
It might look like this, with the bullet just poking out, or – much more likely – it might be invisible.
Why are they bad?
If you try to shoot again with a bullet in the barrel, bad things might happen. I keep a picture of a split-open 1911 barrel near my bench as a reminder to be careful. It was my gun. I sold it and two weeks later the new owner re-arranged its molecular structure.
You might get lucky: some guns will tolerate a squib. Most won’t, and it certainly can’t be good for a gun even if it survives.
What happens when you get one?
Carry around a brass rod and small hammer. Drop the rod in the barrel, and hammer out the squib (take it all apart first to be safe, and be absolutely sure through inspection that it’s just a stuck bullet, not a stuck round).
It’s not so easy with a rifle – who is going to carry around a 24″ brass rod? Some people use cleaning rods, then wonder how to get the whole jammed mess out – the most likely result is splitting the rod on the bullet. Use a proper rod and pound the bullet out from the non-pointy side.
How you you avoid squibs?
Careful reloading technique. As anyone will tell you – and as you’ll read in your commercial reloading manuals – keep your attention focused on what you’re doing.
On a progressive, use a free-flowing ball or modified ball powder to make bridging less likely. Back this up first with good technique, then with a powder check die like the RCBS Lock-Out die or the Dillon Powder Check – if your press has space for one. Don’t waste your time weighing finished pistol rounds to detect a lack of powder – the weight variance in the case and bullet makes the variance of a few grains of powder invisible. When in doubt, break suspect rounds down and recycle your components.
On a single stage with a reloading block, you can visually inspect the powder level before moving on to the bullet seating part of your session.
How do I know when it’s happened?
“Click” instead of “bang”. Now, maybe you have super-human hearing and astounding presence of mind and will hear the “pop” of the primer through your ear protection over other gunfire on the range and/or while stressed during a match. Maybe not, and all you’ll hear is a click. If you think you might have a squib but didn’t hear the “pop”, just stop and investigate. As always in safety, your sense of what is safe is in play – not mine – so govern yourself accordingly.