.223 ammo, also known as .223 Remington or 5.56x45mm NATO, is a popular and widely used rifle cartridge. It was originally developed for the civilian market as the .223 Remington, but it is also the standard military cartridge for the M16 and AR-15 rifles, designated as 5.56x45mm NATO.

The .223 cartridge is a small-caliber, high-velocity round designed for intermediate-range engagements. It has gained popularity among civilian shooters for its relatively low recoil, flat trajectory, and accuracy. It is commonly used for varmint hunting, target shooting, and competitive shooting sports such as 3-gun matches.

The bullet diameter for .223 ammo is .224 inches (5.7mm), and it typically comes in various bullet weights, ranging from 40 grains to 77 grains. Lighter bullets are commonly used for varmint hunting, while heavier bullets are often favored for long-range shooting or competitions.

The .223 cartridge is typically loaded with a bottlenecked case that holds the powder charge, primer, and bullet. The high velocity and small size of the cartridge allow for a relatively flat trajectory and good terminal performance, making it effective for shooting at medium distances.