The .240 Magnum Rimless Holland & Holland (also known as the .240 Apex and the .240 Super Express) is a centrefire sporting rifle cartridge developed in English gunmakers Holland & Holland no later than 1919,[3] primarily for use in hunting deer and plains game.
[1] As it was common for rimless hunting cartridges, a rimmed (beltless) variant, at the time called just "Holland's 240 Super Express"[4] and now sometimes named .240 Flanged Magnum or .240 H&H Flanged, was developed simultaneously for break-barrel rifles and combination guns.
[5][2] The ballistic performance of the .240 H&H in factory loads is very similar to that of the .243 Winchester, with a 100-grain (6.5 g) bullet with a diameter of .245 inches (contrary to the .240 name) giving a muzzle velocity of approximately 2,900 feet per second (880 m/s).
When it is loaded at the same pressure as the .243 WSSM using modern powders, the .240 H&H has the potential for slightly better performance.
Most bolt-action rifles made for the .240 H&H will be amply strong enough to handle hand-loaded cartridges at high pressure.