this was to sold once by Holt's

A MASSIVE 2-BORE FLINTLOCK BALL GUN BY HENRY HADLEY, LONDON, third quarter of the 18th century, with 28in. two-stage round sighted barrel struck with two gold-lined maker's marks at the breech, grooved tang, rounded lock signed 'HADLEY', substantial replacement walnut full stock, military-style brass mounts (side-plate probably replaced), and original iron ramrod (iron parts discoloured throughout), London proof marks, barrelsmith's marks 'H. HADLEY' and 'LONDON'.

Other Notes: This incredible piece weighs in at over 23lbs with each ball weighing approximately 1/2lb. The vendor informs us that the gun was found in India about 40 years ago. The original stock was unfortunately in a very poor state but thankfully enough survived to provide a template for the replacement. Its weight and dimensions would make it a rather impractical weapon from a military point of view, the favoured theory being that this was an early solution for an elephant gun.
Estimate Ł3,500-4,500