It is my understanding that Dum Dum is from the name of the arsenal outside Calcutta where hollowpoint ammunition was manufactured.
Yes, Dum Dum Arsenal, it was the center of the Indian rebellion in the 1850s. I had a few of these, measured the depth of the hollow point and well it's deep @ approx 1/2" to 3/4".
That sucker would explode hitting flesh.
Not my pic, It's from anglo boer war site..


















































