Daryl - Lancaster's largest bore size for the 4 barrelled pistols was .476, later changed to .450/.455 when the British military changed calibres ( I don't know if Lancaster changed the bore size also)

Joel Black, who sometimes posts here IIRC sent me many pages of info including the "Gun" magazine article and Lancaster advertisements of the time

Their largest calibre was .577 X 1 1/2" but I saw a Wilkinson Howdah pistol at an Arms Fair in UK a couple of years ago in .577 Snider - with a load of 70 grains BP behind a 480 grain bullet it must have been quite a handful!!
I should have bought it!

Hope this helps

TH 44