Which features distinguish an assault rifle from an older military rifle?

Assault rifles are distinguished from older military rifles, such as the high-powered bolt-action or semiautomatic rifles of the World War II era, by several key technical features:

• Intermediate Ammunition: Unlike older rifles that used high-powered cartridges, assault rifles are chambered for ammunition of reduced size or propellant charge. This "intermediate" power allows for a lighter, more portable weapon while still maintaining lethal effectiveness at modern combat ranges.1
• Selective Fire: A defining characteristic is the capacity to switch between semiautomatic and fully automatic fire via a selector switch. Older military rifles were typically limited to semiautomatic or manual bolt-action operation.21
• Manageable Recoil: By utilizing smaller cartridges and advanced gas-operated systems, assault rifles produce significantly less recoil than older, high-powered rifles. This makes the weapon controllable during automatic fire, whereas older, heavier rifles were often unmanageable when fired automatically.1
• Design and Materials: Modern assault rifles often incorporate lightweight materials like aluminum and plastic, as well as detachable box magazines, to improve portability and ease of use in close-quarters combat.1