Briefly, the early simple solid lead ball and cylindrical projectiles - being made of soft pure lead - tended to flatten and expand on impact when fired by the old gunpowder (Black-Powder) propellant loads.
Bertie-Clay - working at the Ordnance Department of the British Indian Army, was the guy who in 1896 invented the 'evil' Dum-Dum expanding bullet for the .303" rifle. He was Superintendent of the British arsenal at Dum Dum near Calcutta in Bengal.
There were several 'iterations' of official plus home-made versions of .303" expanding rounds used by British soldiers against enemy forces - who, naturally protested at their inhumanity and effectiveness.
During the Hague Convention of 1899 - Sir John Ardagh explained to an absorbed audience,
"men penetrated through and through several times by our latest pattern of small calibre projectiles, which make small clean holes,' were nevertheless able to rush on and come to close quarters. Some means had to be found to stop them.
'The civilized soldier when shot recognizes that he is wounded and knows that the sooner he is attended to the sooner he will recover.
He lies down on his stretcher and is taken off the field to his ambulance, where he is dressed or bandaged. Your fanatical barbarian, similarly wounded, continues to rush on, spear or sword in hand; and before you have the time to represent to him that his conduct is in flagrant violation of the understanding relative to the proper course for the wounded man to follow—he may have cut off your head."
Ardagh.A very British approach, what !
- There were expanding bullets before Dum-Dum - and certainly afterwards - but "Dum-Dum" has entered into our folk-law books as the archaic name for the expanding bullet.
Bertie-Clay died on 17 October 1938, having lived for some time at Villa La Pensee in Tahiti - down our way in French Polynesia. - Ardagh died in 1907 following a long and most distinguished career (worth Googling).
P.S. While talking about "dum-dums" - I'm pleased to note the return of a very few neighbor Australian mates to my blog stats.. this surely indicates that some aussies are able to read eh.
(- I'm currently recording around a thousand total 'hits' per week.)