The Magpul PMAG M3 AR-15 5.56 30-round Magazine with a window is a popular and well-regarded magazine designed for use with AR-15 pattern rifles chambered in 5.56x45mm NATO or .223 Remington. Here are some key details about this magazine:

1. Caliber Compatibility: The magazine is designed for rifles chambered in 5.56x45mm NATO or .223 Remington. It is a standard choice for AR-15-style rifles, carbines, and pistols.
2. Capacity: The magazine has a standard capacity of 30 rounds, which is the most common capacity for AR-15 magazines. It provides a balance between ammunition capacity and magazine size.
3. Construction: Magpul PMAGs are known for their durable and lightweight polymer construction. The polymer material is resistant to rust and corrosion, making it suitable for various environmental conditions.
4. Window: This particular PMAG M3 model features a transparent window on the side of the magazine. The window allows the shooter to quickly check the remaining round count without removing the magazine from the firearm.
5. Finish: The magazine is typically available in black, but Magpul offers a variety of color options to suit individual preferences.
6. Compatibility: Magpul PMAGs are designed to be compatible with a wide range of AR-15 rifles and carbines. They are known for their reliability and consistent feeding.
7. Anti-Tilt Follower: PMAG M3 magazines often come equipped with an anti-tilt follower design, which helps ensure smooth and reliable feeding of ammunition.
8. Dust Cover: Some versions of PMAG M3 magazines include a dust cover that can be placed over the top of the magazine to help protect the ammunition from debris and contaminants.
9. Availability: Magpul PMAGs are widely available and are used by many shooters, including law enforcement and military personnel.
10. Legal Considerations: Always be aware of and comply with local, state, and federal laws and regulations regarding magazine capacity and firearm ownership. Magazine capacity restrictions can vary by location, so it’s essential to understand and adhere to local laws.

Magpul PMAGs, including the M3 model with a window, are known for their quality and reliability. They are a popular choice among AR-15 enthusiasts and are suitable for various shooting activities, including target shooting, competition, and self-defense. Proper maintenance and regular inspection of magazines are essential for ensuring their long-term reliability.