What component of a muzzleloader is placed over the nipple?

The component of a muzzleloader that is placed over the nipple is referred to as the cap. In muzzleloading firearms, the nipple is a small threaded tube that serves as the ignition point for the firearm. When a cap is placed over the nipple, it contains a reactive material that, when struck by the hammer, ignites and creates a small flash. This flash then travels through the nipple to ignite the main charge of powder inside the barrel, allowing the bullet to be fired.

Understanding the role of the cap is essential for safe and effective muzzleloading practices. The cap must fit securely onto the nipple to ensure reliable ignition. Failure to do so could lead to misfires or inconsistent performance of the firearm. Other components such as flints, hammers, and frizzens play distinct roles in different types of ignition systems, primarily in flintlock mechanisms and do not directly serve the purpose of igniting the charge via the nipple.