The things you find when linking

If you're not a gun-nut this probably won't intrest you.
BUT if you are, here is an interesting history of the dum dum round.

...Eventually the propellant was changed from black powder to the famous Cordite in 1891 or 1892 (references differ as to the exact date of changeover) by means of the “Mark 1 C” cartridge, “C” denoting Cordite smokeless nitro propellant. A few minor changes necessitated by the new propellant resulted in the “Mark II C” cartridge. The same 215 grain bullet now achieved a velocity of 1970 fps, and everyone seemed satisfied.

Everyone that is, aside from those who actually had cause to shoot anyone with this new round and rifle. Good accuracy, yes. Flat trajectory, no doubt about it. Amazing firepower too, from this new magazine fed repeater. This was just as well, as those hit by it frequently failed to acknowledge the fact, and regularly took multiple hits before actually ceasing in the attempt to rearrange one’s internal anatomy with various sharp and unpleasant edged ethnic implements. In the 1890’s the British Army was engaged in a number of operations in the Indian and Afghan theatre, and this lack of effectiveness of the new ammunition was a cause of major concern. The previous Martini-Henry rifle with its 480 grain soft lead bullet had been proven time and time again, but this new rifle just wasn’t up to snuff. When small British detachments found themselves outnumbered ten to one against fanatically courageous opponents who took and gave no quarter, the problem was a serious one. Wound ballistics was a poorly understood science in those days, but even 1970 fps was insufficient for such a smallbore, relatively heavy, round nosed projectile to be effective as a military round. Penetration was fantastic - even up to and including an elephant’s skull - but it was too good on human targets, and energy transmission was virtually nil. Sub - 2000 fps speeds were too low for effective hydrostatic shock and temporary cavitation, all of which the British trooper was finding out the hard way on the field of battle.

As most of this unpleasantness was going on in the Indian theatre, the problem was tackled in situ and was solved at a place whose name must rank as one of the most over-used, misquoted and poorly understood terms in the history of firearms in general and projectiles in particular. The place was Dum-Dum arsenal in India. It was here that the full metal jacketed .303 bullet was changed to one having a small amount of lead core exposed at the tip, creating in effect a soft-nosed bullet which would expand in flesh - as did the previously used Martini-Henry lead bullets - and thus greatly increase its effectiveness. Any hunter having observed the differing terminal effects of solid bullets as compared to soft noses on lighter, thin skinned game will readily appreciate the difference. The .303 and the .450 Martini- Henry rounds were almost identical in their actual muzzle energies, but now the .303 could more effectively deliver that energy to the target. The infamous Dum-Dum bullet was born, and real-life fighting showed it to be far more effective than the old Mark 2 bullet. Troops engaged in savage warfare, but still equipped with the older Mark 2 ammunition, would sometimes file down the tips of the nully jacketed bullets to make them like the “Dum-Dum” projectiles. In those days the Indian contingent of the British army had considerable autonomy in equipment and procurement of same, so while the Indian theatre was equipped with the soft nosed Dum-Dum bullet the same was never adopted by the rest of the British army. The same problem was appreciated, but dealt with in a different way by the adoption of a hollow-nosed bullet called the Mark 3, soon improved and widely manufactured as the Mark 4 in 1897, and the very similar Mark 5 of 1899.

Then we get into all these Liberal whiners about the "Geneva Convention" and the rest of the mis-information peddled by the msm........