US SB597

Raises the minimum age from 18 to 21 for purchasing handguns, semiautomatic assault weapons, large capacity ammunition feeding devices, and ammunition suitable for these firearms

Defines "semiautomatic assault weapon" to include semiautomatic rifles and pistols with detachable magazines plus specific features (pistol grips, folding stocks, threaded barrels, barrel shrouds), as well as an extensive list of named firearms including AR-15 and AK-47 variants

Defines "large capacity ammunition feeding device" as magazines, belts, or drums capable of accepting more than 10 rounds of ammunition

Provides exceptions for individuals under 21 who are Armed Forces or National Guard members in the line of duty, and for temporary transfers with parental consent for employment, farming/ranching, target practice, hunting, or firearm safety courses

Amends 18 U.S.C. Chapter 44 to prohibit licensed dealers from selling these firearms and devices to anyone under 21 and makes it unlawful for individuals under 21 to possess them