If someone were to ask me this question during the 1970s ( when I first began hunting ) , then I would personally opt for the 9.3x62 mm Mauser . This is simply because ( during the 1970s ) ammunition ( and bullets ) for the 9.3x62 mm Mauser were of far better quality than ammunition ( and bullets ) for the .375 H&H Magnum .
The only .375 H&H brand of factory loaded ammunition which one could get ( back in those days ) , were from Winchester Western and Remington Peters . Neither were very good . Let us talk about Winchester first . Their full metal jacket 300 grain solid bullets had flat noses and no steel in the jackets . They were practically guaranteed to break apart , upon striking the bones of Gaur or Asiatic jungle elephant bulls . This was no good . A close friend and former colleague of mine ( forest ranger Abu Sayeed ) actually got killed by a charging Gaur bull , by attempting to use this .375 H&H Magnum ammunition to take a frontal heart shot on the animal . In 1974 ; Winchester altered the jacket material of their patented Silvertip soft nosed bullets from a mixture of copper , nickel and zinc to aluminum ( in order to reduce manufacturing costs ) . The “ updated “ bullet was completely unreliable for hunting anything dangerous . Remington’s full metal jacket 300 grain solid bullets actually employed far thinner jackets than the ones employed in Winchester’s full metal jacket 300 grain solid bullets . And Remington did not manufacture a 300 grain Core Lokt soft nose factory load ( they only offered a 270 grain Core Lokt factory load ) .
The only .375 calibre bullets ( for the hand loading market ) which were available during this time were from Barnes and Hornady . Barnes copper jacketed lead cored solid bullets were quite prone to severe distortion , upon striking the bones of Gaur and Asiatic jungle elephant bulls . Their Barnes Original soft nosed bullets were quite excellent , however . Hornady cupronickel jacketed lead cored solid bullets were also prone to severe distortion , while their soft nosed bullets frequently came apart ; creating only superficial injuries on the intended target animals .
By contrast , RWS manufactured excellent factory loaded ammunition for the 9.3x62 mm Mauser . Their 293 grain RWS TUG soft nosed factory loads were absolutely unrivaled in terms of terminal and ballistic performance . They also used to offer exceptionally sturdily constructed 286 grain steel jacketed solid factory loads ; which could be successfully used against the largest of Asiatic jungle elephant bulls ( even when frontal brain shots were required ) .
Today however ( with the advent of modern factory loaded ammunition and reloading components ) , I would opt for the .375 H&H Magnum in the blink of an eye . It is the bare minimum legal calibre for hunting dangerous game , in most African countries . It can employ a 14 grain heavier 300 grain bullet ( to say nothing of Norma’s new 350 grain factory loads , which employ Woodleigh bullets ) . And ammunition for it , is comparatively easier to find in even those out of the way places .