john 'pondoro' taylor, a transplanted english irishman who somewhat defined the golden age of safari in the waning days of empire [phase one], defines 'big bore' as follows in his seminal book, 'african rifles and cartridges' (safari press, reprint 1994):
"LARGE BORE. A rifle the caliber of which is not less than .450".
"LARGE MEDIUM BORE. A rifle the caliber of which is not less than .400" nor greater than .440" (11.2mm).
"MEDIUM BORE. A rifle the caliber of which is not less than .318" nor greater than .375".
"SMALL BORE. A rifle the caliber of which is less than .318".
"MINIATURE. A rifle the M.E. of which is less than 1,500 ft. lbs.
"MAGNUM. A rifle the M.V. of which is not less than 2,500 f.s.