What is “Cylinder Gap” & what potential negative safety and functionality implications does it have?

Cylinder gap is the term used for the distance between the end of the cylinder and the start of the barrel. These should have relatively tight tolerances to avoid malfunction, damage, and injury. Malfunction can occur if the gap is too large and lead bullets are being fired. The soft metal passing through this gap can shave off the bullet and lodge into this gap preventing your cylinder from rotating the next shot. This can damage the firearm but more importantly the pressures pushing through the same gap may expel dangerous debris such as this metal flake and still burning gunpowder.