Absolutely - note Forsyth's book contains many 'quotes' form notable gun makers and hunters alike. Old W. Greener had a fair handle on things, as did Baker.
Baker notes his 'baby', which many people today think was a 2 bore- wasn't. The gun shot a 3oz. belted ball, "never failed to floor a charging elephant". He had a 4oz. conical made for it "which led me into such scrapes I eventually gave up the conical as useless".

This gun would have been a 5 bore at the largest, probably a 6 bore only due to the extra weight added to the ball in it's belted design.

Note that bore size was exactly that, a measurement of the bore, not the groove diameter, in muzzleloaders.

He (Baker) also noted that "a ball that size (talking about a 14 bore gun, 15 bore ball, just over an ounce) would penetrated both sides of an elephant's head" with a hardened ball, using only 4 1/2 drams of powder. That's only 123gr. No wonder my 14 1/2 bore ball (1.1oz) did so well on Moose with a mere 165gr. of powder.

Books such as this are treasures, indeed.