A Key Loaded Dimension
Overall length, often abbreviated OAL or COAL, is the total length of an assembled cartridge measured from the base of the case to the very tip of the projectile. It is one of the core dimensions defined by ammunition standards because it determines whether a loaded round will feed from a magazine and chamber correctly. Small deviations in this single measurement have outsized effects on function.
Why Limits Exist
Overall length must fall within a defined window so the round works with the mechanism. If a round is too long, it may not fit the magazine or may jam against the rifling before the action closes; if it is too short, it can feed erratically or seat the bullet deeper than intended. Standards therefore publish minimum and maximum bounds rather than leaving length open.
Seating Depth and Pressure
Overall length is set by how deeply the projectile is seated in the case. Seating a bullet deeper shortens the round and reduces the internal case volume available to the propellant, which raises pressure; seating it out lengthens the round and lowers pressure. This link between length and pressure is why published load data pairs a charge with a specific overall length.
Magazine and Feeding Constraints
In repeating firearms the magazine imposes a hard ceiling on length. A cartridge that exceeds the magazine's internal dimension cannot stack or feed, regardless of its ballistic merit. This practical limit is one reason standardized maximum lengths exist, ensuring ammunition remains compatible with the firearms designed around it.
The Ogive Measuring Point
Because bullet tips vary and can be slightly deformed, precision handloaders often measure length to a point on the ogive rather than to the extreme tip. Measuring to a fixed diameter on the curve gives a more repeatable figure, since two bullets can share an ogive position while differing at the meplat. This distinction matters when chasing consistency.
Worked Example
The 9x19 has a specified maximum overall length near 1.169 inches. A factory load might sit close to that figure so it feeds reliably in standard magazines. If a handloader seats a projectile far deeper to shorten the round, the reduced case volume can spike chamber pressure even with an unchanged powder charge, which is why length is treated as a safety dimension and not just a fit dimension.
A Common Misconception
Many assume a listed overall length is a single exact value every round must hit. In practice the standard defines an acceptable range, and factory ammunition varies slightly within it. Just as important, overall length cannot be changed freely to fit a magazine, because altering seating depth shifts internal volume and pressure. Length is a controlled window tied to safety, not an arbitrary trim.