The .350 Legend, also called 350 LGND (9×43mmRB), is a SAAMI-standardized straight-walled intermediate rifle cartridge developed by Winchester Repeating Arms. The cartridge was designed for use in American states that have specific regulations for deer hunting with straight-walled centerfire cartridges. At the cartridge's introduction, Winchester claimed that the .350 Legend was the fastest production straight-walled hunting cartridge in the world, although some .450 Bushmaster, .444 Marlin, and .458 Winchester Magnum loads are faster and have much more energy, and the .350 Legend would be surpassed in 2023 by the .360 Buckhammer. It is designed for deer hunting out to a maximum effective range of 250 yards (230 m).

The .350 Legend shares many characteristics with the .223 Remington, such as an overall cartridge length of 2.26 inches (57 mm) and a rim diameter of .378 inches (9.6 mm).

At the 2019 SHOT Show in Las Vegas, Nevada, the .350 Legend cartridge was introduced by Winchester Ammunition. It was the first new centerfire cartridge announced by Winchester since its 2004 introduction of the Winchester Super Short Magnum series. The Sporting Arms and Ammunition Manufacturers' Institute (SAAMI), the U.S. firearms and ammunition industry's technical standards-setting organization, announced the acceptance of the new cartridge and chamber standard on January 31, 2019.

The cartridge was developed to deliver enough energy to achieve lethal terminal effects on large deer out to 200 yd (180 m). The recoil is said to be less than a .243 Winchester. As of late 2024, Winchester offers six different loads for the cartridge: a 150 gr (9.7 g) Deer Season XP at 2,325 ft/s (709 m/s). a 180 gr (12 g) Power Point at 2,100 ft/s (640 m/s), a 160 gr (10 g) Defender designed for use in the AR-15 platform at 2,170 ft/s (660 m/s). a 145 gr (9.4 g) FMJ in the USA ammo line at 2,350 ft/s (720 m/s), a 150 gr (9.7 g) Copper Impact at 2,260 ft/s (690 m/s), and a Super Suppressed 255 gr (16.5 g) subsonic load at 1,060 ft/s (320 m/s). Several other companies, among them Barnes, Browning, Federal, Hornady, and Underwood, offer various loadings.

The cartridge offers a flatter trajectory with less recoil and better terminal performance over current straight-wall cartridges while remaining compliant in most applicable states.

The .350 Legend cartridge is designed to cycle in a variety of firearm platforms, and has been shown to operate in bolt-action rifles like the Winchester XPR.

.350 Legend has no parent case. However, .350 Legend uses the same 0.378 in (9.6 mm) nominal rim diameter as .223 Remington. The .350 Legend case is a new design that maximizes terminal performance while optimizing the ability to extract the cartridge from the chambers of a variety of firearms. The .350 Legend did not adapt a .223 Remington parent case in order to incorporate a slight body taper (for extraction), as well as additional shellcase length and case volume.^{[citation needed]}

Winchester engineered .350 Legend hunting projectiles (such as the Extreme Point and Power-Point bullets) for use on big game out to 250 yd (230 m). These bullets were designed specifically to maximize .350 Legend cartridge performance.^{[citation needed]}