There is no single answer to the question "What is the mass of a bullet?" Bullets come in a wide range of sizes and weights, depending on the type of firearm and intended use.

Here's why there's no simple answer:

* Caliber: The diameter of the bullet (e.g., .22 caliber, .38 caliber, 9mm) influences its weight.

* Material: Bullets are made of lead, copper, or a combination of metals. The material's density affects the bullet's weight.

* Purpose: Bullets designed for hunting, target shooting, or self-defense have different weight requirements.

To give you an idea, here are some examples of common bullet weights:

* .22 LR: 40 grains

* 9mm Parabellum: 115 grains

* .45 ACP: 230 grains

* .30-06 Springfield: 150-180 grains

Note:

* 1 grain is a unit of mass equal to 0.0648 grams.

* The weight of a bullet can vary slightly even within the same caliber.

If you need a specific bullet weight, you will need to look up the information for the particular caliber and bullet type you are interested in.