I think I got that from another book game records of hunting in africa, I think that was where I got it from. The author corresponded with him not just about the elephants he shot but also buffalo and lions and so forth. He included Bells comments about it all and its all quite fascinating.
I may have run those recollections together, I remember he went out for elephant first with 2 .303's, and I know he was friends with Jeffery the gunmaker in Scotland and he says he was familiar with all kinds of firearms when he was young from shooting them at the range witht he gunmaker when doing his testing.
Bell shot a lot of buffalo for meat for his men, he made mention that the rifle he called a high power .22 was erfectly good at this task at head shooting them. He shot about 50 lions from memory, and he noted that he shot them almost entirely because they were upsetting his porters.
I recall also that out of the 1011 elehpants he shot, I think it was either 50 or 70 were cows, and these animals were almost all shot because they were belligerant.
I will look it up again if you like.