The .223 Remington (often called .223 Rem) and the .223 Ackley Improved (AI) are both rifle cartridges, but they differ in their case design, performance, and intended use. Here are the key differences:

1. Case Design

• .223 Remington: The .223 Rem is a standard factory cartridge with a tapering case and a shoulder angle of around 23 degrees. It is widely used in various applications such as target shooting, hunting, and military use.

• .223 Ackley Improved (AI): The .223 AI is based on the .223 Rem but has been modified by gunsmith P.O. Ackley to have a steeper shoulder angle (typically 40 degrees) and less body taper. This design allows for more internal case capacity, which can hold more powder and potentially deliver higher velocities.

2. Performance

• .223 Remington: The standard .223 Rem is capable of propelling bullets at velocities of around 3,000 to 3,300 feet per second (fps) for typical bullet weights (55-62 grains). Its performance is more than adequate for most shooting scenarios, including varmint hunting and target shooting.

• .223 Ackley Improved: Due to the increased case capacity, the .223 AI can typically achieve higher velocities (about 100-200 fps more) compared to the standard .223 Rem. This improved velocity can result in flatter trajectories and slightly better long-range performance.

3. Compatibility

• .223 Remington: This cartridge can be fired in any rifle chambered for .223 Rem.

• .223 Ackley Improved: Rifles chambered for .223 AI can still fire standard .223 Rem cartridges. When you fire a .223 Rem in a .223 AI chamber, the case is "fire-formed" to the AI shape. However, to take full advantage of the .223 AI design, you need to reload with cases that have been fire-formed and load them to the correct specifications.

4. Reloading

• .223 Remington: Widely available as factory ammunition, .223 Rem is easy to find and shoot without the need for reloading.

• .223 Ackley Improved: Since .223 AI is a wildcat cartridge, factory ammunition is not readily available. Reloading is essential, and you’ll need to "fire-form" the brass by shooting standard .223 Rem in the AI chamber, then reloading the fire-formed cases.

5. Use Cases

• .223 Remington: Commonly used for small game hunting, varmint shooting, and target shooting. It is known for its versatility and availability.

• .223 Ackley Improved: Generally used by handloaders and enthusiasts looking to push the .223’s performance, especially in long-range varmint or target shooting.

Summary:

• .223 Rem is the standard, factory-loaded round with widespread availability and good performance for most shooting needs.

• .223 AI is a modified, handloader’s cartridge that offers more velocity and slightly better ballistics, but requires reloading and brass preparation (fire-forming).