Odd number of shots. Period. Yes I own a bunch that shoot 6, but from a strength point, odd numbers. With even numbers the locking recess on the cylinder is in line with the chamber and is a very weak point in the overall cylinder structure. Think about a 5 pointed star... the thinnest part of the cylinder is at the very top of that highest peak, and is in line with the barrel. The locking portion though is straight down and is in the bottom of the bottom /\ with plenty meat around it. With metals and pressure, things tend to stretch and twist but typically don’t rupture nearly as early if things are consistent, but if you give it a natural weak point it will start to fail there and the failure moves relatively easily. On an odd number gun the cylinders thinnest point is still very uniform and consistent, very strong and not likely to fail without something very serious happening.