Common Shotgun Shell Sizes
The length of a shotshell is normally given in inches and is based on the length of the spent hull. Common lengths for 12 gauge are 2 3/4, 3 and 3 1/2 inch. Some European shells give the shotshell length in millimeters.
You must know the correct length of the shotshell, gauge and shotsize when selecting shotgun ammunition. Go on to learn more about shot.