A comprehensive visual guide to all common rifle and handgun calibers is available as a free download from the catalog request page of the Sierra Bullets website. A requester must provide contact information, including first and last name, email address, mailing address and daytime phone number.
The PDF chart lists each bullet by caliber and diameter in millimeters and shows the profile of each projectile. The projectile at its widest point determines the caliber of a bullet. For example, a 9mm round simply has a 9-millimeter-wide projectile. The imperial caliber system conveys the same measurement as a decimal fraction of an inch, with a 9-millimeter bullet expressed as .355 caliber.