Better known as a “dust cover,” the ejection port cover is designed to keep dirt and debris out of your rifle, and it’s especially important to close the cover when you’re not using the gun. The cover can be used in a variety of conditions, from dry and dusty to rainy and muddy, and it’s a great way to protect your rifle in less-than-ideal conditions.
Depending on your rifle’s lower receiver, the AR-15 ejection port cover might not have a place on a sport upper receiver. These types of receivers typically don’t use an ejection port cover or a forward assist. If you’re not sure whether your upper has an insert for the ejection port cover pin and retaining ring, be sure to check before you try to install a port cover.