Meanwhile, the design team at Holland & Holland were listening and learning. A velocity of at least 2150fps and a sectional density of at least .300 was required for satisfactory penetration on large game. High velocity was a distinct bonus in ensuring hits at unknown range, and that impact velocities of over 2250 fps produced explosive wounds, and often lightning quick kills. Reducing bullet weight, and therefore sectional density, to allow an increase in velocity did not, however, produce the desired effect. Sectional density had to be maintained above .300 in order to achieve acceptable performance on big game, irrespective of velocity. The replacement for the .400/375 had to be a true magnum (ie deliver all available bullet weights at over 2500fps) for marketing purposes. It had to be safe against the largest game, and yet also usable for long range shooting on medium sized game in the mountains of India and Nepal. As the rifle was intended to be suitable for dangerous game, reliability of feed and extraction was of paramount importance, and this dictated a very tapered case with a shallow neck angle. The only way to easily achieve accurate headspacing with such a cartridge was to retain the .400/375’s belt:- the one feature of that already obsolescent cartridge that worked! Finally, it had to be able to work through a standard length Mauser action, since Rigby held the monopoly on magnum Mauser actions.

And so, out of these requirements came the greatest medium bore to date. Sticking to the .375 bore size, H&H increased the bullet weight to 300 grains to bring the sectional density to .305, and stretched the case to the maximum that could possible be accommodated in the Mauser action (a special extra long magazine box had to be used). Velocity was a genuine 2500 fps, and was achieved at a pressure of only 47,000 PSI, an important consideration for a cartridge designed for tropical use. In order to fulfil the requirement for an antelope rifle for use on the open plains of East Africa, a 270 grain spitzer soft point bullet at 2650fps was introduced, whilst for long range shooting in the Himalayas and such places, there was a 235grain spitzer bullet at 2800fps. To cater for the hunter who preferred doubles, a flanged version with the same three loadings was made.

The .375 H&H Magnum was an instant success. It was suitable, in reasonably open country, for all African and Asian game. The 270 grain, or 300 grain soft-nosed loads sorted out large soft skinned game like lion, tiger and eland with panache, whilst the 300 grain solids proved perfectly adequate for elephant, buffalo or rhino under all except the most adverse conditions. Only as a long range rifle with the 235 grain load did the .375 H&H show any shortcomings, recoil was simply too stiff for use in a light mountain rifle. Nevertheless, for the one rifle man, the .375 could certainly do it all from impala to elephant. In a time of constant change and slow, dangerous travel, no man could afford to be without a rifle suitable for dangerous game. Yet the primary quarry would be something for the pot. Few men could carry, let alone afford, a battery of rifles, so the ‘all round rifle’ was a very much more eagerly pursued goal than it is today.

Initially the .375 H&H lagged behind it’s German rival. The 9,3 was available in the superbly built, yet budget priced Mausers, used a cartridge that fitted the standard length magazine box, and utilised a simple and cheap to produce cartridge design that kept the cost of ammo down. Hollands' .375 was a proprietary cartridge, with (best quality and consequently expensive) rifles available only from Messrs Holland & Holland. The belted case design added considerably to the cost of the ammunition. For the discerning sportsman though, or the slightly better off farmer/pioneer, the .375 had a distinct ballistic superiority over its rival (particularly in Kynoch loadings).