The AR-15 forward assist is a spring-loaded button on the upper receiver that pushes the bolt carrier group fully into battery. Shooters press it when the bolt fails to close completely on its own. It helps ensure proper chambering in adverse conditions like dirt, mud, or cold temperatures. The button sits on the right side of the upper receiver and fits standard AR-15 upper assemblies. Builders include an AR-15 forward assist on most standard builds for reliable bolt closure and field operation.