The .244 Holland & Holland Magnumcartridge was created in 1955 in Great Britain by deerstalker and rifle-maker David Lloyd (d. 1996), of Pipewell Hall, Northamptonshire and Glencassley in Sutherland, Scotland, and is not to be confused with the smaller-cased and much milder 6 mm (.244 in) Remington. Stalking on extremely steep deer forests such as his own at Glencassley, Lloyd was in search of a "canyon rifle" cartridge that would shoot exceptionally fast and with a very flat trajectory across deep valleys and over distances out to 300 yards and more, to make range estimation less critical for accurate bullet placement, and to deliver a hard-hitting bullet weighing a minimum of 100 gr. The .244 H&H Magnum easily met these criteria.
. That load and velocity remain standard for the commercially-loaded cartridge today; although handloaders can achieve higher velocities with careful load tuning. The .244 seldom performs well in barrels less than 26 inches (Expression error: Unexpected < operator.
long, owing to the need for a longer bore to allow pressure and bullet velocity to reach intended levels.
Lloyd was unable and unwilling to embark upon commercial cartridge production, and consequently "gave" the cartridge to veteran London rifle and ammunition makers Holland and Holland Ltd., who in 1954 had paid him £250 towards his cartridge development costs. H&H quickly adopted it, the cartridge acquired the prestigious "H&H" appellation, and both H&H and David Lloyd went on to build significant numbers of very high-quality bolt-action deer-stalking rifles in .244 H&H Magnum calibre (see Lloyd rifle). Initially, commercially-loaded ammunition was manufactured by IMI Kynoch at its Birmingham, England factory. Commercially, this cartridge has only ever been loaded with 100-grain (Expression error: Unexpected < operator.
bullets: lighter- and heavier-bulleted loads have been created by handloaders.
Chuck Hawks, a prominent US commentator on rifle cartridges, opines that, "the .244 H&H Magnum represents some sort of high water mark in the development of the 6 mm cartridge. To use an aviation analogy, you could think of it as the Concorde of rifle cartridges." 
David Lloyd, the .244's originator, went on to develop a still more powerful prototype round by reducing the case body taper and increasing the already large power capacity to produce the "David Lloyd 6 mm Magnum". His hope was to use bullets heavier than the .244 H&H standard 100-grain; but this cartridge was never commercially produced, and only two prototype Lloyd rifles are believed to have been chambered for it.
In the early 1990s British fieldsports author and ballistician Colin McKelvie had a custom rifle built on a BRNO CZ Magnum action, with a .244in Border Barrel with a 1:7 fast twist. Using handloads with very-low-drag (VLD) .244in hollow-point bullets of 115 grains (7.5
, accuracy of 0.63 MOA was achieved, with average muzzle velocity of 630ft/s(1,106m/s)and acceptable chamber pressures. This level of performance is what Lloyd had sought with his "improved" .244 H&H Magnum.
While the belted .244 H&H Magnum could be considered the velocity/energy pinnacle of 6 mm/.240in cartridges, that power comes at the cost of significant muzzle blast, as well as shorter-than-average barrel life; in addition to which commercially-loaded ammunition is expensive. Because of these drawbacks the cartridge never came into widespread popularity, and has never been offered as a chambering by any of the mass-market riflemakers. The .244 H&H rather fell by the wayside in favor of 6 mm rifles in the same general class such as the .240 Weatherby Magnum (for which it had been an inspiration to designer Roy Weatherby), and also the various 6.5 mm Magnums. The .244 H&H still has its adherents, however, and occasional rifles are still chambered in this caliber, by Holland & Holland and others. Ammunition is still made for Holland & Holland, and used cases can of course be handloaded.
Such extremely high velocity calibers always invite controversy, and the .244 H&H has been passionately condemned (invariably by commentators with little practical experience of it) as a result of some reports of rifles blowing-up or seriously malfunctioning as a result of massively excessive chamber and bore pressures. A few such incidents have occurred; but the fault in all cases has been found to lie with the rifles' owners' failure to keep the bores scrupulously free of accumulated copper fouling. The very fast, rapidly spinning .244 bullet tends to deposit bullet gilding metal fouling rather readily, especially in a roughly bored barrel, and as this deposition builds up the bore becomes constricted and internal pressures rise exponentially, sometimes to and beyond danger point. Accurate and safe shooting with the .244 H&H - an extreme cartridge - has always been predicated upon meticulous bore cleaning, which is essential. Where this has been done, no rifle has failed to perform well and safely.
Despite the .244 designation, the .244 H&H Magnum actually uses a bullet of .245in diameter, similar to its older, much milder H&H predecessor, the .240 Apex; and this has been a source of some confusion, and of frustration to handloaders. Most typical 6 mm caliber cartridges use a .243 bullet. While there is a wealth of market choice for the handloader seeking good .243in diameter hunting bullets, such as are used in the .243 Winchester, the .245in bullet is only made in one 100-grain type, exclusively for the commercial manufacturers of this cartridge. Attempts to use conventional .243in bullets in a H&H or Lloyd barrel bored for .245 have been disappointing, with indifferent accuracy. However, a few enthusiasts have achieved very good results with custom-made rifles, using .244 H&H chamber reamers on barrels bored to .243in., using standard .243in bullets.